Remove the following 6 screws:

One 3 mm Phillips on the right side of the fan.

One 6 mm or 7mm Phillips on the left side of the fan.

Four 8mm or 9 mm Phillips securing the heat sink to the lower case.

On Santa Rosa/Penryn models (photo 2), the heat sink has a slightly different screw pattern.

On Early and Mid 2009 models (photo 3), the heat sink has yet another slightly different screw pattern.