Well, it's more difficult to update it through DOS, of course. If you want to do it with a USB drive, you need to read up on how to make a bootable USB drive, or if you want to burn it to a CD, you need to make the CD bootable. After that is easy though. Just run BIOS_DOS.bat from the DOS folder once you get booted into DOS.
And if THAT doesn't work, I really have no more ideas for you.