I don't know whether you need to enter BIOS to change the boot order before loading the operating system. Perhaps others could advise you. If the BIOS default allows you to load the operating system and you are using Windows 8, you could finish your build, load Windows 8 and enter UEFI BIOS from Windows 8 as explained in the Gigabyte FAQs. Then make any changes you require. I don't know whether other operating systems have this facility.