Replacing drum brakes isn't difficult but it does require special tools and a mistake could kill you. It is not recommended that you attempt to repair your own brakes. This is for educational purposes only and hopefully will convince you that the price charged by a trained mechanic is well worth it.
So here’s how to replace brake drums:
Remove the hubcap and loosen the nuts.
Jack up the car and support it with jack stands. NEVER work on a car supported by a jack alone. Blocks of wood or bricks or even cinder blocks aren't suitable substitutes.
Finish removing the nuts and remove the tire.
Spray the hub of the wheel with penetrating oil (PB Blaster - WD-40 is not a penetrating oil!).
Grab the brake drum by the edges and try and pull it off.
Note: some brake drums are held on with screws so you will need to take them out.
Once the drum is off take a look at it. It should be refaced or replaced if it is scored.
Spray the whole brake mechanism with brake cleaner. The dust from most brakes is ASBESTOS and you don't want to breathe it in, so wear a mask.