The preferred method is to flash your BIOS using the DOS interface. To accomplish this:
1. Determine which way is supported (floppy or USB)
2. Download the BIOS update to the media determined in step one.
3. Restart computer
4. If you saved the BIOS update to a floppy, it will load automatically. If your BIOS supports updating from USB, you must enable the option to boot from USB first.
Generally, the update is an automated process, but you likely have to confirm the update before the said process begins.
If the update gets interupted in DOS mode (and the only way it can is if the system is shut down or restarted) then you would have to redo the update because the BIOS will likely be corrupted due to the incomplete update.
With Windows; however, the problem is more severe. Should you use Windows to update your BIOS and the update is interupted, you may have a non-bootable computer, resulting in you having to redo the update, but in DOS mode anyway.