Replacing a Ryobi 10-inch miter-saw blade is easy if you follow some basic concepts. The key to it is to make sure the blade isn't bigger than 10 inches or thicker than the factory-supplied blade. If it's too big, it can come into contact with the blade guards, and if it's too thick, it will stop the blade bolt from properly securing it.
Unplug the saw. This is a safety consideration and a very good idea.
Remove the screws in the center of the lower blade guard. Rotate the lower blade guard and blade bolt cover-up. The blade bolt will be exposed.
Press the spindle lock button and rotate the blade bolt until the spindle locks.
Loosen and remove the blade bolt--clockwise--using the supplied wrench.
Remove the flat washer and the outer blade washer. Leave the inner blade washer.
Drop a little oil on the inner-blade washer and the outer-blade washer—just where they contact the blade.
Slide the new saw blade onto the spindle. The teeth should point downward at the front.
Replace the outer washer and the flat washer. They will align using double "D" flats.
Replace the blade bolt--counterclockwise this time--while pressing the spindle lock button.
Tighten the blade bolt, replace the lower blade guard, replace the screws and tighten everything.