Dell OptiPlex 755 User Manual page 230

1 module locking switch
3. Press the device latch release so that the latch release pops out.
1 device latch release
NOTICE: Do not place any heavy objects on top of the computer. Doing so may bend the chassis and cause difficulty in removing a module device.
4. Pull the device by the latch release to remove the device from the module bay.
1 latch release
5. Slide the new device into the module bay.
6. If desired, you may lock the new device in the module bay by moving the module locking switch to the locked position (you must remove the computer
cover to use the locking switch).
7. If you removed the cover to lock the device in the module bay, replace the computer cover (see
Removing and Installing a Device When Your Computer Is Running Microsoft® Windows®
Replacing the Computer Cover).