Like John mentioned, use a hammer, but baware if you doing the rear ones, as these can be a little tougher. The p-brake shoes sometimes want to hold onto the inside of the disc, and that requires some additional monkeying.

But, if you're doing the front, hammer away (assuming you're replacing the discs), or if not, use a dead blow or brass or lead hammer to get them off without marring the disc.

BB