There are two ways to upgrade the USR-G806 firmware, webpage or USR upgrade cable. In most condition, you can use webpage to upgrade firmware. If some fault cause you can not open webpage of G806, you should use USR upgrade cable to upgrade firmware.
To upgrade G806 via upgrade cable, you need contact USR sales for special cable. Then connect the PC to G806 LAN port via Ethernet and connect PC to 806 with USR USB cable.