Need a diagram of oil change on a 2005 Chevy Cavalier

Diagram? The drain plug is on the bottom of the oil pan on the engine toward the rear of the pan. Simply remove that with an adequate container under it and drain the oil then replace the plug. Next remove the oil filter which is usually located on the bottom side of the motor that exact location varies but I believe they put it on the passenger side front of the engine at the bottom in 2005 to give you more room to reach it. depending on what type of filter is there now the color will vary but should clash to some degree. Fram -Orange, STP -Blue/White, Mopar Stock and some off brands White or Black. It will look like a canister. Dab your finger in new oil and make sure you coat the seal on the new filter before you screw it back in place. Screw it down hand tight then 1/4 turn extra. Remove the drain fill cap from the valve cover and fill with the proper type of oil. Use 4 quarts initially is you change the filter, if you don't then add 3 and 1/2 quarts of oil and check the level after 2 minutes and top off till the level is between the add and full marks on the dip stick. Most likely your vehicle uses 2W20 oil either synthetic or regular oil, your choice. I recommend Penzoil for 2005 vehicle but it is your choice.

You probably have the 2.2L ecotec engine. The oil filter is what they call a canister filter. It is located just below the fill cap under a cap/housing with a 36mm head. The o-ring on the housing/cap should be replaced with the filter. The drain plug is on the bottom of the engine on the oil pan and can be loosened with a wrench (either 13mm or 15mm depending on which drain plug was installed at the factory)