1.Remove the brake caliper from the wheel knuckle that it's mounted to. Be sure to support it on something or with a wire hanger so that the brake hose doesn't get damaged.
2.Remove the outer brake pad but leave the one on the piston side attached.
3.Retract the screw on your disc brake piston tool and slide its plate into place where the outer pad used to be, lining the retracted screw up with where the piston is behind the other pad.
4.Use the attached handle to screw the screw part of the tool towards the pad. As you do this, you will see the piston-side pad begin to retract.
5.Do this until the pad is flush with the caliper, ensuring the piston is fully retracted.
6.Remove your disc brake piston tool and the piston-side pad.
7.Once the caliper has been retracted back into its bore, you can move on to installing your new brake pads and rotors, which will now easily slide over each other. Be sure to press the brake pedal a few times before moving the car, to re-seat the pads against the rotors.