The easiest way I update the bios on my Asus board is to use the Asus EasyFlash2 under tools in your bios.
Instructions.ASUSTeK Computer Inc.-Forum- EZ Flash 2 - the safest way to update BIOS This avoids having to do it in windows>turning off any Av programs creating a bootable flash drive ect.
In the instructions it says to rename your bin file but I just flashed mine and didn't need to rename it. Fabe