Replacing it with a new one? Then just carefully shove the outer part sideways a little and it will pop out (and probably break.)
Otherwise, it has some tabs that are difficult to press to release it from the dash, because it's almost impossible to get your hand in there to do it. Once you have it separated, the other half can fall down behind the dash so you can reach in and unplug it, then pop the new one in.
They're pretty cheap at the parts house. Like $6/each.