if the drums have been on there awhile, it can be hard to remove them. there can be a lot of rust build up or the shoes could have wore a lip in to the drum, so the shoes will have to be backed out with the star adjuster. if adjusting the pads does not help then you will need to get some PB Blaster and a hammer. a last resort which is a rarity is getting a drum puller and pull the drum off along with all the hardware behind it.
just remember to do one side at a time so you have a reference when your putting the one side back together.