Besides downloading the BIOS file, you also need the flash utility to flash BIOS ROM. (For files before August 2001)
You won't need to update BIOS until the latest bios has improve / fix some functions.
You won't need to upgrade through all of the BIOS files, just upgrade to the latest one please and it will include all previous improvments.
The CMOS data will be lost after flashing the BIOS. You may need to enter the BIOS setup screen and configure your system information after rebooting the machine.
Note: Some download management or acceleration software may cause issues with file downloads. Please disable any download management software if you experience problems downloading a file.