I've recently installed Altezza brakelamps to my 1999 Altima GXE. Here is a quick removal and install guide:

Tools needed-
5/16 socket
1/4in socket wrench
1/4in extension
Flat head screwdriver
Phillips screwdriver


Removal
Open the trunk and carefully start removing all the hold down tabs that hold the lining in place around the brakelights.

You'll need your phillips for this if you still have the factory tabs, if you break some, don't worry about it as most car parts stores have these for cheap.

After you remove the tabs hold back the lining and locate the 4 nuts that hold the brakelamp in place. 3 are easy to find and the 4th is where you will need your extension.

Remove the bulbs from the brakelamp housing, usually the large bulb with the green stripe wire is the blinker, the other large bulb is the brake light and the small bulb is the reverse light.

Once the nuts are off you will need to use a flat head to pry (carefully) around the outside of the housing, it will start to come out. Be aware of a lot of black adhesive that was holding in the housing.

Installation
Be sure to place the new brakelamp housing and foam gasket in place with the black adhesive that is already there, it will form a good sealant.

Line up the 4 bolts with the existing holes and push them into place then attach and tighten all the nuts.

Return the bulbs to the proper location. It may be necessary to splice in an additional length of wire to the reverse light bulb (the small one) as it may not reach into the new housing. Don't worry about cutting and splicing a new wire in, it will not hurt the electrical system or the function of any of the other bulbs, etc.

Done. Have a beer.