If you don't feel like opening your case:
The Maximus series allows you to put any version of the BIOS on a usb key and install it when the PC is powered down. The section in the table of content is 'BIOS update utility' (page 2-13 for the Extreme version).
Essentially, download your BIOS to the root directory of your USB key, rename it to M8E.CAP. Power down the system. Insert usb in the bottom usb that is blue inside and below the PS2 plug. Press and hold the button named 'BIOS' on the left side of the rear connectors until the light starts to flash. Power up the PC when the light stops flashing.