dude its SIMPLE..
STEP 1->U need to know the company which motherboard u r using..
note-->VIA,NVIDIA, etc are just chips..manufacturer means something like ASUS,INTEL,MERCURY,MSI etc etc...
STEP2->Once u got ur manufacturer go to its website.I think its easy to do.
STEP3->Find the link which says something like "PRODUCT UPDATE /SUPPORT/DRIVERS" etc etc
STEP4->Locate ur model number on that page
STEP5->Obtain the updated version of ur bios(if any) and instructions how to update it.
P.S->some companies make the use of floppy drives necessary.However some companies like INTEL provide .exe of updated bios which u can double click and install..only thing to make sure is that there shud be no power cut during the update process .U can locate the manufacturer name and model no of ur motherboard on its cover box itself...