1993 Ford F250 Rear Brakes locked

You need to back the starwheel adjuster off, there is an adjustment hole in the back side, it will require the use of a brake spoon and a thin awl or screwdrive, push the adjusting lever away from the starwheel and back the adjustment off until the drum can be removed.

sometimes i have noticed that they have a tendency to rust and freeze on there, especially the heavy duty modles.

if after what merlin says doesnt work for some reason

then it is probably frozen on and you can heat it up with a torch and hit it firmly untill it breaks the rust free.