I guess what I would try is to squirt some penetrating lubricant between the pad and the shoe, let it set for a couple of hours, then put the shoe in a vise with the open end down (cushion it with blocks of wood or a towel, and clamp only tight enough to hold it), and use a punch and soft hammer to try to knock the pad out.

If you use any lubricant, make sure you clean the shoe thoroughly with brake cleaner or soap and water before installing the new pad.

Also, there will probably be residue from the old brake pad on the inside of the shoe. Take that off with Scotch-Brite and brake cleaner, or if you use a petroleum-based solvent, again make sure you clean it off completely.