Gently pry it out, it just snaps in. You will have to remove the adjusting lever and interior trim to unplug the heater cable.
When you put the new one in, make sure the tab sticking straight out behind the glass goes into the spring slot instead of bending over to one side.
VERY easy fix, easier that the interior mirror.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!