I just completed this task for replacing one of the left rear brake light bulbs. Open the storage / CD changer (if so equiped) compartment in the left rear of the trunk. There is a 5.5-6 inch flap located in upper part of the left side of the door opening that you bend out toward you to expose the tail-light / brake light assembly. I had to use a knife to cut two small remaining attachment points of this flap - one on top and one on the bottom. When you bend the flap back you can see the rear of the assembly and you will notice 4 white tabs clipped into red snap-in points. Simple press the white tabs towards the center of the assembly to release them from the snap-in points and then you can wiggle/jiggle the bulb panel out and replace the bad bulb(s).
To replace, wiggle/jiggle the bulb panel back into place and press the tabs into the snap-in points until they click into place. Fold the access flap back into place and close the storage / CD changer (if so equiped) compartment door.