The right rear tire on my wife's Toyota Rav4 slung its tread and beat the crap out of the car. The tail light was busted. We ordered a replacement from eBay for twenty bucks, a good deal. I replaced the lens when it finally got in but had to get a new bulb. Here's the way to pull the lens off and replace the bulb or the lens, same thing.
Removing the lens is a simple matter of three screws. First there's a screw holding a small cover beneath the lens. Next there's two screws at the bottom. Don't drop them! With screws removed pull out on the lens. It will pop out. You'll see a pin that fits into a snap fitting. Lean the lens out. Carefully twist the light socket counter clock wise and pull out. Replace the bulb. Obviously if you're replacing the lens you have to switch the three lights to the new one. One at a time, don't get them mixed up.
Here's what a tire tread can do to a tail light.