Read the instructions and perform the install how they tell you. There should be an icon for gigabyte on your desktop and the bios updating should show there
If you have the bios update utility in windows you can do it that way. It will either have an icon on your desktop or it will be in your gigabyte folder in windows
There are different BIOS updates depending upon what board revision you have. Look at the top of the screen to the gigabyte link I gave you because that is where you choose which update your board needs.