Bios update is totally unsupported, continue at own risk!
The bios must be flashed through efi shell, there are multiple guides online on how to do this, here's a quick summary of how to do this.
Note: This may or may not work, only to give you an idea on how its done.
Note: The quotes are not ment to be typed.
Download the appropriate bios file for your device, uncompress it to the root of your USB thumb drive, rename the bios file to "BIOS" so the full filename should be "BIOS.bin" next boot into EFI shell, select your file system (USB thumb drive). For example type "fs0:" or "fs1:" and press enter, make sure your bios files are located there, now type:
"afuefi BIOS.BIN /p /b /n /x /l /reboot"
Then its gonna flash & restart