Make sure you have your emergency brake off, and you will probably need an old bat or 2x4 to hit the rotors from behind to loosen them after removing the disc retaining screw. If they still don't come out spray lots of WD40 through the lug nut holes and around the hub to loosen. Once you det the rotors off make sure your hub is clean so the new rotor sits flush once installed. I use a wire brush with penetrant to brush off old grease and corrosion.