Dell Dimension U7021 Owner's Manual page 105

On the retention base locate the
b
tab opposite the power supply.
Press on the retention base tab
until the heat sink pops up
slightly.
Press out on the second retention
c
tab while lifting the heat sink up
and out of the retention base.
NOTICE:
Lay the heat sink down on its
side.
NOTICE:
If you are installing a processor
upgrade kit from Dell, discard the original
heat sink. If you are not installing a
processor upgrade kit from Dell, reuse the
original heat sink and blower when you
install your new processor.
6 Push down and out on the socket
release lever.
heat sink
retention tab
retention base
Removing and Installing Parts
105