Attach a 10mm socket to a ratchet.

Make sure the back of it is turned to loosen rather than tighten. If there is noise being made when rotated up, that is tightening. Turn the knob at the back to change to loosening.

Place the ratchet on one of the bolts and start rotating the ratchet down then up to loosen each nut. After each nut is loose remove them by hand.

Keep each nut for reassembly. Also, when removing the last nut, hold the mirror to prevent it from falling.