you can either: 1. get an impact gun to loosen it(or they have a tool that you use with a hammer that acts like an impact gun). 2. if its too stripped to remove, just drill it out(you need a bit that is the same diameter of the threads; compare to the new screws) and becareful not to go all the way through. you just want to drill the head of the screw off. once you drill it out, the rotor will come out and the threads from screw will be left in there. just use a pliers and unscrew it. some penetrating spray might help. as for the new screws they should come with your new rotors or just get them from the dealer.