Exploded diagram for your SM100M miter saw is
here.
User manual is
here.
Page 20 covers blade change operation.
Make sure you unplug your saw! You need to remove a screw from the cover and rotate the cover to the rear. Use a hex wrench in the motor shaft to keep the saw blade from turning, and loosen the arbor nut with a 1/2" wrench. The arbor is reverse threaded, so you'll turn it clockwise to loosen, then counterclockwise to tighten it up after you have swapped the blade.
Rotate the cover back after that's done, and replace the screw.
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