If your Subaru Impreza has been making grinding noises when you apply the brakes, it's probably time to change your brake pads. This should not be avoided as worn brake pads could be a threat to your safety, or eventually damage other companents of the braking system. Changing the brake pads yourself will greatly reduce the cost of having your Impreza serviced at a dealer.
Purchase a brake pad kit that matches the year of your Impreza. These can be purchased at an automotive supply store, or from any website that carries Subaru replacement parts. Brake pad kits include new brake pads for each wheel as well as lubricant.
Use a jack to lift the car onto jack stands. Raise the car by cranking up the jack and place the stands underneath the car to keep it raised. Be sure to follow the safety instructions that came with your jack. Remove the wheel by loosening the lug nuts. After you remove the wheel, use a pair of needle-nose locking pliers to removet the cottar pins that hold the large brake pad pins intact.
Tap the larger brake pad locating pins lightly with a hammer until they slide out. Remove the old brake pad.
Use an old pad to push the pistons to one side so you can remove the other old pad.
Use the lubricant that came with your brake pad kit and spread it along the pad's backing plate, along the first shim and along the sides of the backing plate. If you are provided with a lot of lubricant, be liberal in your application. If your kit did not come with lubricant, you can purchase some at an automotive supply store.
Reinsert the brake pads into their proper location and push the locating pins back in. Insert the cottar pins back into place. You should start on the side where the locating pins slide in because they will hold the first pad in place while you work on the second.
Repeat for the three remaining wheels.