Originally Posted by Ferdman

spree17, only replace the rotors if they are near or below the minimum thickness, or they are warped.

It's possible that you could free a sticky caliper piston by cycling it several times. Fully retract the piston, install the worn brake pads then press the brake pedal so the brake pads grip the rotor. Repeat several times and see if the piston gets easier to retract. If not, then you will need to replace/rebuild the caliper.