R&R two screws on front rotors

Here is the deal. You can try a huge phillips bit and a wrench to crack them open. I would suggest a little "liquid wrench" sprayed on first and let soak in. Another that works real well is an impact screwdriver. Very cheap that you hit with a hammer to force the screw to turn.

If by chance you twist them off you can drill them out and retap OR as a last resort skip the screws and as is obvious the rim easily holds the rotor in place.