There's two screws on the front plate next to the dvi port that have to be removed. Once those are removed, as well as all of the screws on the bottom, it should just lift up from the back. I had to pull a little harder than I was comfortable with to break the seal of the thermal paste, but...
I found this thread googling about excessive temps on this card. My temps were almost identical to the OPs, so I did the same thing and removed the cooler. Like his, the die probably 20% or so shiny where no paste had been touching. Cleaned it off, replaced it and now still idling kind of high...