ok, you need to get a special tool to turn the piston back in. or a large flat screwdriver can turn it in - there should be notches on the face of the piston. as for your front brakes, you need to bleed the brake system of air cuz by loosening the bleed screw you may have introduced air in the brakes. this can cause reduced brake response and safety issues. you need to use a large c-clamp to push the piston back in for the fronts.