Follow the instructions in your motherboard-manual.
For some you need to boot from a floppy and update BIOS, for others you can do it from within Windows. As long as you follow instructions, it's easy.
Unless you have a serious issue and the BIOS-update specifically addresses that issue, you should leave it alone.
E.g. my mobo runs on BIOS #17 and #26 is out! I have no need to update.