How do you remove the cover on the rear brakes?

it can be a real pain. they get stuck good sometimes. there should be a hole in the back on the bottom. you stick a screwdriver in that hole and rotate the little gear that's inside. this is also how you adjust them. but mostly you just pound on the drum (cover) with a hammer until you knock the sucker loose.

I'm guessing that you are referring to the rear drums. The shoes should be loosened in order to clear the lip due to drum wear. There is an adjusting hole in which you would use an adjusting tool (or flat blade screwdriver) to rotate a star-wheel (gear) to back off the shoes (if the brakes get tighter, rotate the other direction). Depending on model and design, the adjusting hole may be found on the front of the drum or behind in the backing plate (look for a rubber plug).

Once the shoes are backed off, if you have only minimal rust build-up on the hub, the drum should just slide off with minimal force. Rust build-up can be broken loose with penetrating fluid and hitting the drum face (between the wheel studs) with a hammer (take care not to hit the studs). Also light tapping with a hammer on the sides of the drum near the front should help break any remaining rust free. Try to avoid hitting from the rear or side with any rear force or you may risk cracking the drum (if you are replacing it, then you can hit as hard as you want).