The firmware update process for AVRs consists of loading unzipped files onto a USB key (obtained from the Arcam website), inserting the USB key into the back of the receiver, and pressing Info and Direct keys to start the update process. The update process occurs in three stages, which should be automatic, rolling from stage 1, 2 then 3 autonomously.
Sometimes it gets stuck between stages, displaying a "please wait" screen, which appears to last indefinitely.
Pull out the USB key, and reinsert straight away. The update process should continue.