First, unscrew the six screws that are holding down the fan and heat sink with a Philips #1 screwdriver. Then use a Phillips #1 to remove the single screw near the bottom of the heat sink.

Six Silver Chrome 5.8mm Phillips #1 screws

One 5.8mm Phillips #1 screw

Remove the four screws that are holding down the CPU (the four to the top left that form a rectangle in this image) first. Unscrew them in an X pattern (eg. top left screw, bottom right screw, top right screw, bottom left screw) to minimize risk of harming CPU.