Hi, I'm Pitt, a Professional Tech. This is my very first post, so I fig I might as well make it a helpful one. The drums are getting pressure applied to them by the brake shoes/pads being pushed against the drum surface, and eventually making a groove which the shoes run in. its like a ditch almost. so first, know how they apply the pressure. There are a series of arms and wedges that push the shoe more and more as it ages, they dont retract when you let off the pedal. So in order to get them to release, the post above is correct. You need to go through a view hole in the back or front of the drum, using a small flashlight at firs. You will notice a spring going through a metal arm, pulling at arm down, causing the shoe to hold pressure. You then need to use an awl, ice pick or strong screw driver, to stick into the hole where the spring is attached to the arm. push the pick/awl, the opposite direction that the spring is pulling in and therefore, retracting the brake shoes. Once they release, a light tap with a hammer, or no tap at all, will allow the drum to come off.
At this point, let me give you the BEST advice ever.. TAKE A PICTURE! it looks simple, but replacing these arms and springs properly, gets confusing. the trick is to have a good pic of where it all belongs.
PM me if you need a hand
Pitt