Those screws are crap. They never should have been invented. The wheel holds the rotor on just fine. To get the screws out first squirt some penetrating fulid on them, squirt alot actually. Let it sit a while, half hour maybe. Use a hammer and tap the screwdriver into the screwhead to help seat it well. Sometimes some valve grinding compound helps give it some grip. Try unscrewing it. If no luck, you CAN drill them out. However, I'd go to a local auto parts store and buy a cheapy impact driver. Should be about 10-15 bucks. It's basically a screwdriver that turns when you smack it with a hammer. Very useful for removing these types of things. If still no luck, go ahead and drill them out. You don't need them anyway.