Depends - do you need to keep them?
These rotors tend to rust very securely in place. Soak them in WD-40 or PB Blaster or similar at least overnight. Then, if you don't need to re-use them, don't be shy about helping them off with a few taps from the hammer. If you are replacing the wheel bearings as well, knock the h--l out of them with a hammer. If you want to keep the rotors, heating them around the center with a propane torch helps a little.
On the rear rotors, you may have to reach through the hole with a small flat blade screwdriver and loosen the adjuster on the parking brake to get the rotor free from the parking brake shoes. BTW, your parking brake is not set is it?
If you are replacing rear wheel bearings, the rust holding your rotor on is nothing compared to the rust holding your rear hubs on.