Dell OptiPlex E1 - Manual (Page 56)

Front-Panel Insert Removal (Mini Tower Chassis): Dell™ OptiPlex™ E1 Systems
To remove a 5.25-inch front-panel insert, follow these steps:
1. Hold the bezel with the front facing you.
2. From the front of the bezel, use your thumbs to press 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.