Dell Dimension 4700 Series Service Manual page 29

CAUTION: The heat sink can get very hot during normal operation. Be sure that the heat sink has had sufficient time to cool before you touch it.
5. Remove the heat sink:
a. Remove the retention module clips. Press the tabs toward the center of the clip and lift up.
b. On the retention base locate the tab opposite the power supply. Press on the retention base tab until the heat sink pops up slightly.
c. Press out on the second retention tab while lifting the heat sink up and out of the retention base.
NOTICE: Lay the heat sink down on its side.