from memory, the pistons screw back into the caliper rather than push back. this is because the handbrake acts on the rear calipers. look closely at the flat surface at the end of the piston and you wil find slots machined into it. wind the piston back with a special socket which should be available from where you bought the brake pads. i assume thats what you want to do ! good luck
paul hale, February 2005