The mirror is held in place by a plastic attachment backing for adjustments, and a cable connector for the auto-dimming plus heated functions.

Tilt the mirror fully down, then use your hand if you can to pop it out from the plastic backing BUT do not pull outwards too forcefully at once (don't just yank it out with brute force). If you break the wire connections, it's going to cost a lot to replace the whole assembly! Detach the wire connection, then replace the glass.