If your receiver cannot connect to the internet (servers for 2012-era devices are sometimes deprecated), you must use a USB stick.
Warning: Denon discontinued direct download links for the E300 in 2023. You will likely need to contact Denon Support directly and request the AVR-E300_xxxx.zip file, as most community links are dead. Denon Avr E300 Firmware Update
Steps if you obtain the file:
The Denon AVR-E300 "E-Series" receiver was marketed as an entry-to-mid-level solution for home theater enthusiasts, featuring early integration of Apple AirPlay, internet radio, and 3D video pass-through. Unlike modern AVRs that receive frequent over-the-air feature additions, the E300’s firmware lifecycle was primarily focused on stability and compliance. If your receiver cannot connect to the internet
Firmware updates for this device serve three critical functions: Steps if you obtain the file: The Denon
If your receiver is behaving erratically (frequent freezing, audio dropouts), perform a microprocessor reset before updating: