I want a step step of fixing up the orin brand toilet bowl

hi Patricia.
Overview Toilets haven't changed much in the last 80 years. After a flush, water still fills a tank, lifting a float that shuts off the water when it reaches a certain level. A lever still opens a flapper to cause the flush, falling back into place when the water level drops. So it's no surprise (nor any consolation) that we face the same flush problems today that our grandparents did. Sometimes the flush is too wimpy, sometimes the toilet keeps running, and sometimes the bowl doesn't refill.
Our ace plumbing consultant has a simple four-step strategy to solve 95 percent of these problems. You can complete the first three steps in five minutes. That'll solve most problems. The fourth step is usually easy too, but not always. More on this later. These steps work for most toilets but not for pressure-assist models.
Check the fill tube

Overflow tube problem

Push the fill tube firmly onto the fill valve. Make sure the fill tube sends water into the overflow tube.Remove the tank lid and find the fill tube. It's a small flexible tube that runs from the fill valve to the overflow tube. While the tank refills, this tube squirts enough water down the overflow tube to refill the bowl after the completed flush. If this tube falls off or the water stream misses the overflow tube, the bowl won't fill and your next flush will be wimpy (that is, won't develop a strong siphon). Reattach the fill tube and make sure it perches about 1 in. above the rim of the overflow tube. Flush the toilet and watch the water stream to make sure it goes down the overflow tube.
Adjust the fill height

Check the float

Adjust the float to set the water level. Pinch the clip and slide the float up or down on the rod. Keep adjusting the float until the water shuts off at the proper level.The water level in the tank is controlled by an adjustable float. A float that's set too low produces a weak flush; if it's set too high, water spills into the overflow tube and the fill valve won't shut off. The toilet keeps running. Look for the fill level mark on the inside back of the tank and mark it on the overflow tube so you can see it more easily. If you can't find it, measure down about 1 in. on the overflow tube and make a mark. Then flush the toilet and see if the water reaches and stops at that mark. If not and the toilet keeps running, adjust the float up or down. If you have an old toilet, you'll have to bend the brass rod that connects to the float ball to make adjustments. But with newer toilets you usually turn a screw or slide a clip along a rod. Flush the toilet after each adjustment.
Also make sure that the water level is at least an inch below the C-L (critical level) marked on the fill valve. You can adjust the height of many valves to raise or lower the C-L.
Occasionally the fill valve simply won't shut off, which means that it's defective. If so, turn the water supply off at the shutoff under the tank. Buy a replacement valve (sold at hardware stores and home centers). You don't have to match the old one; many, like the one shown, fit most toilets. It's a 15-minute change-out.
Adjust the flush handle/flapper chain

Flapper chain fix

Adjust the chain to leave a little slack with the flapper closed. Then cut off the excess, leaving about an inch.A chain that's too short or tangled won't allow the flapper to close and water will continue to leak into the bowl. This causes the fill valve to cycle on and off to refill the tank. A chain that's too long, or a flush rod that hits the the tank lid, won't open the flapper wide enough to stay open for the full flush. You'll find yourself having to hold the lever to complete a good flush.
To avoid these problems, adjust the linkage in the chain to leave only a slight bit of slack when closed. Cut the chain at the rod to leave only about an inch extra to reduce the potential for tangles. Then put the tank lid back on and make sure the flush rod doesn't strike the lid when you press the lever. If it does, bend it down slightly and readjust the chain.
Replace the flapper

Change the flapper

Unsnap the old flapper and take it with you to the store to find an exact replacement. In addition to the closest replacement, pick up a "universal" type.If you've completed the first three steps and your toilet keeps running, chances are you have a worn-out flapper. Turn off the water, remove the old flapper and take it to the store to find an exact replacement. (Hardware stores often carry a wide variety.) Most flappers snap over ears on the overflow tube. Others have a ring that slips over the tube.
Now here's the catch. You may not find an exact match. The range of flapper styles has mushroomed over the last 15 years, and you may find 15 to 20 flapper options on the store shelf. Some packages include specific brand and model information (so note yours before you leave home). Others have a "universal" label. If you can't find an exact replacement, try the closest one and pick up a universal type as well. They're cheap, and the extra one just might save you a second trip to the store! (Avoid the "adjustable" types unless you're replacing an adjustable one.)
Install the new flapper and make sure it opens and closes freely. Then test it. If the toilet keeps running or runs intermittently, you're not getting a good seal. Try a different flapper if the toilet won't stop running.
If you just can't find a flapper that seals, consider replacing the entire overflow tube/flapper. On most toilets (two-piece), this means removing the tank. It's not difficult and you don't need special tools. It'll take you about an hour, and you'll avoid that expensive plumber service call.
if you go to this link it will show you step by step on how to fix it. How to Stop Running Toilet Family Handyman

check to see if waster continues to run into the bowl after the plunger has returned to stop water flowing. If it is a slow leak then replace the flush washer on the stopper plunger.

check the overflow pipe in the cistern tank as some fill valves do not stop completely but allow input of water after the noise has stopped. This allows the water level to rise up and the water to flow out into the toilet bowl. Reduce the water level height by adjusting the cut off level and when the water rises past the new level the increase pressure on the valve will shut it off.

Sounds like the vacuum breaker is leaking. By small bowl at the top you mean the part that sticks up above the back of the toilet? If so, that is the vacuum breaker.

The bowl is filled up with the little hose inside the tank, it locks inside of the overflow drain. And runs water in there as it flushes to swirl the water and fill the bowl. Water seeks it's own level, and the level in the bowl is at the top of the trap. It has to hold water, unless it isn't filling or it is leaking. Check out the filler and hope the bowl doesn't have a crack in it. Hope this helps.

Check the fill tube in your toilet one easy way to see if it's leaking is get food coloring and pour in your tank to color the water this makes it easier to see and squeeze the tube in the tank when it's full if you see the colored water running down the middle of it you have a winner! if not you can look around for it sometimes the plastic under the flapper gets cracked too

First off,If the air vent was clogged the toilet would back up and overflow and when it did flush, it would make a gurgling sound.
secondly the water level in the bowl is not important as long as it covers the opening,The water is only there to keep out sewer gases so they don't enter your home and the shape of the trap will always maintain the proper amount of water needed to prevent this.
The previous water level may have been due to a partial clog that has since been removed.

First, fyi, adjusting the knob? in the tank, or the fill level will not increase the amount of water in the bowl. The bowl fills to a certain point, and then as more water is added it starts to go over the built in trap, and down the drain. When you flush the toilet, all the water in the tank dumps into the bowl, and the existing water is pushed over the trap and down the drain. All of this being said it sounds like you may either have an internal crack, between the bowl and trap; you may have a crack that is draining under your toilet, (water spots?), or you have a more serious plumbing issue, improper venting, which is causing a vacuum, and pulling the water out. Hope this helps.

If very little water is used on initial flush, The bowl is functioning as a tank for second thorough flush. The high water level cannot stay high in the bowl while in motion or you would have a mess ion start and stops.

The water level in the bowl is limited by the height of the internal trap down stream from the bowl. There is no adjustment possible. If the problem is odors, you can either flush more often, turn on the exhaust fan, or buy a different brand or model of toilet.