Lift car and set on stands safely. Remove wheel and caliper. Remove the two screws holding the rotor to the hub and scres in two 8X1.25mm bolts to press the rotor off the hub by turning them evenly to get the rotor off straight. Some penetrating oil is useful and some light raps with a mallet to help loosen and remove it. Clean up the corrosion which had it stuck so bad and use a little light grease or anti-sieze on the mating surfaces to prevent the rotor freezing to the hub in the future.