you unscrew the light bulb and put another one in from auto zone. There sholud also be a manual that came with the car (alternatively see if you can find it online) which should help you with the work.
Pull the carpeting behind the brake light. Unclip the assembly, replace bulb.
To change a side light bulb on an Audi TT, remove the light lens by unscrewing the screws holding it on. Then, remove the old bulb and insert a new one. Replace the cover and tighten the screws.
It is not a serviceable part.
I've written it up here... http://samboutros.wordpress.com/2007/04/02/2003-audi-a4-bulb-replacement/ Steps, pictures and links to bulbs...
howto change 2007 kia spectra parking light
The brake light bulb on a 2007 Cadillac CTS can be replaced by opening the truck, removing the rear cover, and disconnecting the wiring harness. The bulb can then be twisted, removed, and a new bulb put in its place.
Open bonnet, remove anything in your way to the rear of the headlight (air ducts, battery, etc.), remove rear panel from the light, replace bulb, use small hands.
How do it replace the stop light bulb
3rd brake light or rear brake lights?
You need a double element bulb.
with your hands ?
To remove the cluster to get to the bulb, lower your steering wheel and remove the trim piece. Take out two screws and pull out the instrument cluster.