Asus P8Z77-V PRO/THUNDERBOLT - Manual (Page 131)

ASUS P8Z77-V PRO 4-17
Chapter 4
3. After the utility detects a new BIOS
firmware, save the BIOS firmware by
clicking from the Save to field,
select the USB flashdrive, and click
Download.
4. After the download is complete,
click OK.
After you download the BIOS file to your flash drive, you can update the motherboard’s BIOS.
Refer to 2.3.11 USB BIOS Flashback for details.