How do I change the back brake light of a Hyundai Elantra?

If it is the light in the rear window, there are two plastic caps on either side on the base of the light. Pop off the cap and remove the screws inside. That should allow you to get to the bulb. I went to autozone for the bulb w/o removing it and they gave me the wrong one. If you have the bulb removed, you're better off, if not, the people at advanced got me the correct one without any issues. If it's the brake lights on the back of the trunk, you access those from inside the trunk. On either side, there are thumbscrews (sometimes under the fabric lining flaps). Once you remove the bulb carrier, you'll know which one is out. It usually lines up with the red cover but if you can borrow someone's time, have them look in your trunk at the bulbs as you test your parking lights to see which one lights and which one doesn't. Hope this helps.