Optimus 120-1995 - Manual (Page 6)

2. If you attached the metal strap, release it.
3. Push the sleeve keys into the slots on the right and left of the
front panel (with the tab facing up) until you hear a click.
4. Pull the keys out and down to remove the stereo.
Note: To remove the sleeve keys from the slots, press the RELEASE buttons
located directly below the slots on the bottom of the unit.
5. Disconnect the wiring harness and the antenna cable.
6. Reconnect the battery's negative (-) cable.