If your brake pads are worn down and need to be replaced, you'll first need to push the caliper back with a C clamp. Here's how to do it:
1. Loosen the lug nuts on the wheel that you'll be working on. Then, jack up the car and remove the wheel.
2. Locate the brake caliper. It's the large metal component that houses the brake pads.
3. Place the C clamp around the caliper, making sure that the jaws of the clamp are evenly positioned.
4. Slowly tighten the clamp until the caliper starts to move. Continue tightening until the caliper is fully compressed.
5. Remove the C clamp and set it aside.
6. Remove the old brake pads from the caliper.
7. Install the new brake pads.
8. Place the C clamp around the caliper again and compress it until the pads are snug against the rotor.
9. Remove the C clamp and re-install the wheel. Lower the car and tighten the lug nuts.