Compaq 247320-003 - Deskpro 4000 - 5166 Model 2500/CDS Reference Manual page 124

5. Use the hand hold to slide the panel to the back of the
computer about two inches and lift out to remove.
The configuration label located on the inside of the side
panel provides additional expansion slot and switch
setting information.
To replace the side panel, complete the following steps:
1. Put the side panel in place so that the tabs fit into the slots
at the upper and lower edges of the panel.
2. Slide the panel into the closed position.
3. Fasten the three thumbscrews on the rear panel of the
computer to secure the side panel.