If the back side of the glass has a big circle in it, it comes out like this:
Using the button on the console adjust the mirror so that the top of the mirror is closest to you. You will see a spring clip barely visible on top of the mirror.
Detach the mirror by using a thin screwdriver to pry the spring up, while gently pulling the top of the glass towards you. Disconnect the two heater wires.
To install the new mirror push the bottom of the circle in first, then the top.

Harry