i need to replace a window motor

well this is going to make me sound dumb but i need instructions on how to replace the window motor in my '91 pontiac firebird. it is the original motor, so the way it is mounted in there is a bit unusual. they screwed it in to the frame of the door and cut the tops of the screws off, and replaced it with a round nut of some kind that ive never seen be for. can anyone help?

If that is the original motor, they are held in with rivets. You have to drill them out to replace the motor. there are two ways to reinstall ...Use a professional rivet gun that does 1/4 inch rivets (cost of tool over $200.00 un less you can borrow one) or use 1/4 in. nuts and bolts. Be carefull when you remove the motor from the regulator , its spring loaded...use vise grips while you drill those rivets out.