Bad brake pads, if not replaced on time, can cut deep grooves in brake discs, making the brake repair more costly. Sometimes, the discs can simply be removed and refinished to remove the grooves, but the discs have a minimum thickness that must be met. If the discs have grooves that can't be refinished, you need to change the brake discs, and you likely need to change the discs on both sides.
Prepare the car by draining half the brake fluid from the master cylinder with a siphon and disconnecting the negative battery cable. Raise the vehicle's front end on jack stands and remove the wheels with a lug wrench. Block the rear wheels to keep the vehicle from accidentally rolling.
Separate the brake caliper from the disc by removing the upper and lower mounting bolts. Hang the caliper somewhere away from the disc with a strong wire--never let the caliper hang by its attached brake hose.
Pull the brake pads out of their shims and clips on the caliper mount, and discard them. It is likely they need to be replaced if the brake disc needs changing. Remove the caliper mount from the disc by removing its bolts.
Pull the brake disc off of the wheel hub. If it's stuck, insert bolts into two of the open holes on the disc and tighten them with the wrench to make the disc pop loose.
Remove all glaze from the replacement disc by rubbing it in circular motions with sandpaper or an emery cloth. Install the disc onto the threads on the wheel hub.
Install the caliper mount onto the brake disc. Remove the shims from the mount and apply an anti-squeal compound to their backing plates before reinstalling them. Install new brake pads into the shims. Connect the caliper back on its mount, compressing the caliper pin into its bore with a C-clamp first.
Reconnect the wheels after both brakes have been changed, and lower the car. Refill the master cylinder to the required level with fresh fluid, then reconnect the battery. Apply the brake pedal multiple times until it feels firm, thus setting the new brakes.
Some vehicles do use disc brakes on the rear wheels. The procedure for changing them is essentially the same.
Look through a repair guide for your specific model vehicle, as little details can differ with each vehicle. This is especially true of the required torque for all the mounting bolts.