Go to the product page for your mobo online. There should be a "support" or "downloads" page, go there and find the latest BIOS revision and download it. Copy it to a USB drive formatted as FAT32. Boot into your BIOS (usually press Del or Esc while PC is booting to get to BIOS). There should be a BIOS update tool somewhere in the BIOS, run that and select the new BIOS from the USB. If your computer turns off for any reason in the middle of a BIOS update, it can brick your computer, so if you live somewhere that's prone to power outages or anything like that it can be a good idea to use a UPS.