It's very easy and inexpensive.
Loosen the screw (look from underneath) that holds the arm to the piece glued to the glass. Disconnect the wire for the light and remove the mirror and arm. A small metal part will be left on the glass. It is attached to the glass with a very thin, clear, double-sticky tape. You can get this metal piece off by working a razor blade under it.
Then purchase a windshield mirror repair glue kit. Reglue the part you've cut off wherever you want it. I moved mine about 5 inches to the right so you view rearwards just over the passenger's left shoulder. (I've also installed lower seats.)
Before you do any of this, loosen the screw and remove the mirror, then move it around (perhaps have someone actually hold it against the glass) to see where you want it. I think just going lower isn't what you want, but moving it to the right will help remove the blind spot. Good luck.