Dell OptiPlex E1 - Manual (Page 44)

Expansion-Card Cage Removal (Low-Profile Chassis): Dell™ OptiPlex™ E1 Systems
To remove an expansion-card cage, follow these steps:
1. Rotate the lever toward the back of the computer until it stops in the upright position.
2. Lift the expansion-card cage up and away from the computer.
To replace an expansion-card cage, keep it flush against the chassis to ensure that the lever engages the notch in the chassis when the lever is depressed.
If reinstalling an ISA expansion card into the expansion-card cage, be sure to slip the end of the ISA expansion card into the plastic ISA expansion-card end support.
The ISA expansion-card end support should not be removed; however, if it is accidentally removed, reinstall it by first inserting its top tab into the side support hole and
then sliding the bottom 2 tabs into the 2 support holes on the chassis floor.