I have a 2002 Trailblazer and have had the light asselbly out several times to replace bulbs. Assuming they didn't change the design, you can perform the operation practically toolless.
I am writting this from memory....
First, pull the grill assembley from the front. There are two clips on top of chasis which slide up to unlock the headlamp assembly. I can provide pictures where mine are located if you can not find them. The clips slide up about 1 inch and release from pins on the assembly. It took me awhile to locate these clips when I first needed to replace a headlight. Do not use anything to pry the clip as it can break the plastic supports. (Been there... It does not affect the remounting of the assembly if you do this...)
Once free, you can twist the bulb assemblies from the housing to free the old assembly. The side marker/turn signals leads are short and have to be relased last.
Feel free to send me a private email and I can post the pictures from my Trailblazer.
Here's some additional reference I recently found: