Huh? Normally it's a (.ROM) file. Only use a BIOS from the OEM site and NEVER anyone else's website; some so called BIOS files are infected files and/or insert a BIOS virus!
Q - What MOBO?
Q - What CPU?
Q - If this is an OEM then what Model? ; OEM it's best to use their tools. The BIOS often lacks more accepted BIOS level + Flash Drive methods.
Q - Why do you feel you need to update the BIOS?