The inside mirror is held to its bracket by screws. Usually these are covered by a colored plastic housing which must be removed for access. These covers can be stubborn; take care not to gouge the plastic during removal.
Once exposed, the screws are easily removed. The mirror mounts are designed to break away under impact, thus protecting your head and face from serious injury in an accident.
Reassembly requires only common sense (which means you can do it wrong-pay attention); make sure everything fits without being forced and don't overtighten any screws or bolts.