Look inside your trunk. There should be a black plastic covering with a little notch that you could put your finger in. Pry that out and it should reveal 4 little bolts (looking at the new taillights could help you find where they're at). Might be a little difficult to see with all the wiring in the way.

Pull out the bulbs first (turn them counter clockwise and pull out) then undo the bolts for the taillight. Installation is the reverse of removal.