Of course, you can use the official way to update the firmware.
But also here the program which allows to update firmware without internet connection.
Author: SoulTaker
Home Page: http://deus.lipkop.club/ (no longer supported)
Direct link to download

Warning!
This software IS NOT an OFFICIAL updater and is intended for use solely for informational purposes.
The author is not responsible for any damage (material, moral, or other) caused to you or third parties resulting from the use of this software. All the steps you are at your own risk!
How to Use
- Run the file dou.exe and wait for the update (internet connection must be available).
- Turn off all your headphones.
- Turn on the remote control WITHOUT the USB cable.
- Go to update mode (Option > Configuration > Update > Confirm).
- Connect the single USB cable between your PC and the remote control (don`t use the recharge cable with 3 mini USB).
- Follow the further prompts of the program.

My name is Paul and I am the founder of Detector For Metal, a dedicated resource for metal detecting enthusiasts seeking to uncover historical treasures and connect with the past using the latest technology. As a stay-at-home dad and family man, I’ve found metal detecting to be the perfect hobby that combines family adventure with historical learnings for the whole family.
As a father, I’m deeply committed to passing on this hobby to the next generation of detectorists, starting with my own children. I share advice on everything from metal detecting with kids to exploring the top 10 metal detecting sites you never thought about. My methodical approach to the hobby goes beyond the thrill of discovery—it’s about creating family traditions while preserving history and sharing the stories of those who came before us.