the motherboard manufacture should be printed on the motherboard, along with model number. with this info, got manufacture motherboard website, and there should be instructions, for any certain program you might need, and what type of "bios" file you might need. normally the files are located on same page. and perhaps 1 to 3 additional linked pages of step by step instructions which you can normally print out.
some are for windows, some are for linux/unix, some are for usb drives. personally would favor the usb drive method. and making sure you make a backup copy of current bios before updating.
if the system is dell, gateway or like computer were manufacture put individual components together, and not a (custom/diy built...