Dell OptiPlex E1 - Manual (Page 62)

Expansion-Card Cage Removal (Mini Tower Chassis): Dell™ OptiPlex™ E1 Systems
To remove the expansion-card cage, follow these steps:
1. Rotate the lever toward the back of the computer until it stops in the upright position.
2. Slide the expansion-card cage out of the computer.
To replace the expansion-card cage, align the tabs on the left and right sides of the expansion-card cage with the slots on the back and bottom of the chassis. With the
securing lever in its extended position, slide the expansion-card cage into place.