brake pad retaining spring tool
The brake pads have strong anti-rattle/locating springs holding them in place. They fit into a recess in the pad and have to be dislodged.
The left hand side of the tool frees the spring. Place the tool in position and then lever the spring up and out of the pad and then let the spring locate on the aluminium caliper. Remove the old pad and insert a new one and then re-locate the spring ensuring that the pad is seated correctly.
The right hand side has a knife edge. Press this in between the back of the pad and the disc face and lever the piston back. Make sure that you undo the bleed nipple half a turn, as brake fluid will come out. Collect this fluid. Don't forget to tighten it again when finished. Top up any fluid loss and then test the brake pedal to seat the new pads onto the disc face.