Remove several of the plastic fasteners holding the carpet to the inside of the lid. Gently force the carpet over the trunk latch assembly. Located under the carpet are ten (10) 10mm nuts holding the lamp assembly in place.
The whole light/license plate recess assembly will come off. You may want to replace ALL the bulbs now instead of later. Two each of: Sylvania 7528 (P21/5W), Sylvania 3157LL, and Sylvania 194LL.

I had one bulb go out on my 2000 STS a couple of years ago. And I did what you suggested, and replaced ALL the bulbs, so I wouldn't have to tear that all apart again! :)

Moving this to the tech tips forum...