Pull the little rubber plugs in the backing plates and back off the adjusters, if you have not done that yet. This should allow the shoes to retract. Then take a bfh and tap on one side while pulling opposite with your hand, going around the drum. If it rusted on the lugs or at the center, WD40 it, and tap a lot.
Worst case, you can cut the drums off with a torch, and just buy new ones.