Removing the lid from a used can of paint can be hard to do since the paint in the rim acts to glue the top in place. The solution is to place a plastic grocery bag over the can before replacing the lid. The double layer of plastic allows the lid to separate easily the next time the can is opened. Draping a piece of cloth on top of the can when you hammer on the lid will keep the paint from splattering. Use a block of wood to protect the rim from denting.