Assuming you took all the screws off (including the small one) they are still stuck probably due to rust. You can brake the rust seal with a hammer hitting the rotor between the threaded screws (do not hit the screws, protect them temporarily with the lugnuts on). A couple of strong but well targeted hits should do and rotors should come off. Also do not hit the edge of the rotors where the pads rub especially if you plan to reuse them.
A little PB Blaster/Sea Foam around the center and some heat ( propane torch is lots hot enough) and some tapping will work the blaster etc. into the rust that's holding it there and should come off. Also beware of E Brake things like King says . Wash thoroughly with brake cleaner before re-use.