Retainer washers neet to come off as mentioned and you may need to get some rust buster and try squirting it where the studs come through the rotors. Tap all around the rotor hub area with a hammer for several minutes to loosen rust. Avoid hittint the rotor if you plan to re-use at all. Another trick is to have someone push outward on the rotor while you tap the studs with a hammer. (use a nut to protect the threads.)
