These can be little buggers to remove, but with a little patience, some jiggling, and finesse, it will come out. If you look at my photo (radio is upside down) you can see the locking mechanism at rest. When the key is inserted in the proper direction (as shown in photo) the "wedge lock" draws into the chassis, allowing you to remove the unit. Sometimes you need to gently manipulate the unit left-right, in-out to free it up. DO NOT pull unit with extreme force or the wedges may become permanently messed up. Good luck!!