There wasn't a voltage change option in the manual.
http://europe.giga-byte.com/FileList...gmf-9-rh_e.pdf
Did you try ctrl+f1 while in the bios, this can reveal hidden options. It's mentioned on page 30. Probably not there, but worth a look.
This page gives the changes addressed by the various bios updates to your board. Unless it's just not mentioned, no sign of it.
http://www.gigabyte.com.tw/Support/M...ProductID=2294