If you have searched for the term you are likely experiencing one of three things: a notification prompting an update, a specific bug or glitch (like HDMI handshake issues or Bluetooth dropouts), or you are preparing a factory-fresh setup.
You can set your AVR-X520BT to automatically check for updates. Go to and set it to ON . The receiver will check for a Denon AVR-X520BT firmware download once per day in standby mode. Denon Avr-x520bt Firmware Download
While this model does not receive the frequent HEOS streaming updates seen in newer units, firmware patches for the X520BT typically address: If you have searched for the term you