Unless there is a specific problem you're trying to fix, and you know for certain that the BIOS upgrade will fix that, do NOT do a BIOS update. This is nothing like apps version updates or driver
updates. If something goes wrong during the BIOS update, your machine is turned into an electric brick.
My advice to folks is to NOT do any BIOS updates unless you are sure of the following:
1) You have a way to store off the current working BIOS code to a media that can be used to restore it
2) You have a way to restore that saved BIOS code if the update goes badly.
That said, ASUS board I have used in the past had something known as EZ-flash (or something like that) that involved you booting with a special key combination that then launched a BIOS update utility. You could then stick in a diskette or a USB stick and save off the current BIOS. IF that utility still exists with your motherboard, it will be explained in the manual that came with it.