Once opened up, you'll see the battery sticker. Peel back the sticker and disconnect the battery cable. See the breakdown review for better pictures on removing the battery cable.

Luckily, to remove the heatsink, you don't have to remove anything else except for the battery cable and screws holding it down.

After the battery is disconnected, note the locations of the screws on the heatsink. there are 4 screws around both the CPU and GPU along with a screw at each end of the heatsink

The screw on one end of the heat sink has a rubber cap. Remove the cap to access the screw.