You will need a USB drive that is formatted to .fat32. The firmware file can be found on our website under the downloads section of the unit you have or the firmware and downloads page (https://anthemav.com/support/latest-software.php).
Once downloaded the file will need to be extracted from the zip folder and placed on the root folder of the USB mentioned previously. Insert the USB with the file into the Front USB port beneath the panel door, power the unit on, and press and hold the Select button for ~3 seconds (this will initiate the update process, alternatively this can be initiated from the Setup menu).