Dell OptiPlex E1 - Manual (Page 39)

Front-Panel Insert Removal (Low-Profile Chassis): Dell™ OptiPlex™ E1 Systems
To remove a front-panel insert, follow these steps:
1. Lay the computer cover upside down on a flat work surface with the front of the cover facing you.
2. From the front of the cover, use your thumbs to push inward on the insert until it slides off the 2 posts.
To replace a 5.25-inch front-panel insert, position the 2 ring-tabs over the posts on the inside of the bay opening, and then press the ring-tabs over the posts. If
necessary, use a 1/4-inch nut driver to help push on the ring-tabs.