Go to the gigabyte website, make sure you have the right version MB ( rev.3.1, rev.1.4, etc), then downlaod the BIOS and unzip the BIOS to the USB drive, also download and install the utility called @BIOS, then following the on screen instruction, update the BIOS. Here is the info.
http://www.gigabyte.com/webpage/20/HowToReflashBIOS.html
And I recommend use the #2 @BIOS, A Windows-based BIOS live update utility. If you can use the "UEFI", insert the USB with the BIOS you downlaod, then click the " update BIOS from file" (note don't use the "update BIOS from gigabyte server") , redirect the link to your USB drive, then update the BIOS.