Hi Richard,
I broke mine in two the first time I did it...had to order a new one from Volvo, it was 30.00. You have to gently pry the edges out from the reflector side of the light at each bottom corner (be VERY careful), and once you get the cover off, look underneath the light, you will see a black plastic tab, gently lift it with a flat screwdriver, and slide it towards the front of the car, it will get to the end of it's track and pop off. Once you do that, look at the inside housing, you will see two plastic tabs, press these in at the same time, and pull the cover away. the bulb is an 1156 Osram. (single terminal, single filament)BE SURE TO PUT DIELECTRIC GREASE ON THE BASE OF THE BULB. Turn the old one to release it, insert new bulb. Line up the black internal cover and snap it into place. Then, line up the base of the light in the grooves of the bracket attached to the package shelf. Push it to the rear of the car (you will feel it ratchet into place.)Line up the plastic decorative cover and gently push it into place, it will lock when properly installed. Hope this helps, and good luck. Just remember the plastics are very brittle. Cheers! Dave