Most of these radios have a frame that slips into the cubby. There are tabs you bend outwards to keep the frame from being pulled out of the cubby. The radio slides into the frame and clips to its sides.

If the radio has a removable face, it probably has a couple of slots into which you fit a particular tool to release clips keeping the radio from sliding out. Some models have tabs extending from the sides of the case of the radio. Push in the tabs as you pull out the radio.

If that doesn't work, see it you can get a knife or similar object between the radio holder and the frame (top and bottom) of the console to push down the tabs holding the frame in place. the tabs usually bend up from side to center so start with the knife in the center and slide it to the sides. With the ashtray out, feel the bottom of the radio for the tabs so you have a better sense of what you're up against.

Sixto
95 S420
87 300SDL