If the update fails twice in a row, your unit is likely "end-of-lifed." At that point, it is cheaper to buy a used replacement on eBay ($100–150) than to pay for a bench repair.
: After the restart, navigate back to Firmware > Check for Update . It should display "No update required. Latest version installed". How to update my Denon AVR - Find Answers Denon Avr E300 Firmware Update