It can be very risky. The Basic Input-Output System (BIOS) is stored on a chip on the motherboard. It acts as the communication device between a computer's hardware and its operating system. Without the BIOS, the PC's operating system would have no way to communicate with, or take control of, the hardware. So if the BIOS is fried, toasted, terminated with prejudice, etc there's no way to load the operatng system. HowStuffWorks "How BIOS Works"
If the BIOS hasn't been fried, toasted, etc it might be possible to reset it to factory specs. How To Clear CMOS (Reset BIOS)
One other consideration is that since the BIOS resides on the motherboard, it can't be backed up in a traditional way with a restore point or system image. They only work on the hard drive information. If you're not having any problems with the BIOS, it might not be worth the risk to update. On the other hand, most computer manufacturers have worked closely with BIOS manufacturers to make the update process as simple as possible. Almost as simple as a Windows Update. But even that
isn't a 100% sure thing. People post on the Forum almost every day how a Windows Update hosed their computer,