Compaq 247320-003 - Deskpro 4000 - 5166 Model 2500/CDS Reference Manual page 123

The Compaq Deskpro 4000 and 6000 Series of Personal Computers
include features that make it easier to upgrade or service your
computer.
To install optional equipment, you must remove the side panel
and front bezel to gain access to the expansion slots or drive
bays you want to use.
To remove the computer side panel, complete the following
steps:
1. If you have locked the Smart Cover Lock, use Computer
Setup to unlock the lock.
For more information about Computer Setup, refer to
Chapter 8, "Using Compaq Utilities."
2. Turn off the computer and any external devices.
3. Disconnect the power cord from the power outlet.
4. Facing the back of the computer, loosen the three
thumbscrews on the side panel. Use a coin to loosen them
if they're too tight to loosen by hand.
!