Consult your owner's manual or the local auto supply store for the correct replacement bulb size. Once you have a new bulb, pop open your trunk. Look behind the brake light panels for accessible openings to the bulbs. You won't need to pry off the red lenses or anything.. . Reach inside the opening and twist out the bad lamp (bulb). It may just pop out if you give it a half-twist and pull up. Once the old lamp (bulb) is out, put the new bulb in by reversing the process. Stick it in the receptacle and twist it until it locks into place. Test it by having someone press on the brake pedal while you watch for a light, or park the car in such a way that the rear brake lights reflect off a wall. You should be able to see if the lights are working by looking at the wall in your rear view mirror.