Not the easiest upgrade I've ever done (perhaps the most difficult, actually), but I got it done. Removing the keyboard was the trickiest step for me. Be patient. If you can work one of the corner releases, you can put a flat-blade screwdriver under the corner of the keyboard and work on the other releases (starting at the far corner, then the centre).
The other tricky problem I had was getting the little ribbon cable for the trackpad properly reconnected after completing the project. (I thought the keyboard cable would be the tricky part, but it turns out to be pretty easy.) Be patient and you'll be fine. You may want to test (with a mouse handy) before you reinsert the keyboard.
