The radio has a slot on each lower left and lower right corner of the front face.  Obtain the Mercedes tools (see images), slide them into the slots until you hear/feel the tool snap into place.  The curved edge faces inward. 

Pull the tools outward; if the radio is stuck, alternate pulling left & right in a wiggle fashion to release the radio.  1993 model Mercedes often require the ashtray to be removed to allow the tools to insert fully.

Remove the tools by inverting the radio and pushing on the clips of the radio.  This will release the tool from the radio; pull the tool out.

Disconnect the wiring harness and antenna and plug them into the new radio.  Depending on model, your car will have the ISO plug, a plug for the CD changer, the fiber optic cable, and antenna. 

Slide the new radio into the slot until it snaps into place.  Don't push on any of the buttons!