Dell OptiPlex GX400 User Manual page 31

Your microprocessor uses a zero insertion force (ZIF) socket with a lever-type handle that secures or releases the microprocessor.
To remove the microprocessor, pull the socket lever straight up until the microprocessor is released. Then remove the microprocessor from the socket
(see the following figure).
Removing the Microprocessor
7. Install the new microprocessor in the socket:
a. Ensure that the lever on the microprocessor socket is fully extended to the release position.
NOTICE: When you place the microprocessor in the socket, ensure that the microprocessor aligns properly with the socket. You must position the
microprocessor correctly in the socket to avoid damage.
b. Align pin 1 of the new microprocessor with pin 1 of the socket.
NOTE: Pin 1 of the microprocessor is indicated by a small dot or a triangle in one corner of the microprocessor. Pin 1 of the socket is indicated by a
small triangle in one corner of the socket. See
c. Carefully set the microprocessor in the socket and press it down lightly to seat it.
d. Rotate the socket lever back toward the socket until it snaps into place, securing the microprocessor.
Replacing the Microprocessor
8. Install the microprocessor heat sink:
NOTICE: If you are not installing a microprocessor upgrade kit from Dell, reuse the original heat sink and securing clips when replacing the
microprocessor.
"Replacing the Microprocessor."