The Web interface has no “off” button (it probably should). So, having given it some thought, here is a safe method for upgrading:
You probably installed duplicacy in /opt/duplicacy/
You probably trimmed the long filename to just duplicacy, and will do so again.
You probably have duplicacy set to run automatically at boot or login.
These instructions will assume you did all these things when you first installed duplicacy.
Wait for any running backup to finish, or stop it using the web interface. Stopping it won’t break anything.
In a command console enter:
killall -i duplicacy
This should ask you if you would like to kill the duplicacy process which is still running in the background. You may need to run this as root (sudo). Answer yes to killing duplicacy.
To be extra safe, you can now rename the old version. In your command console, go to the duplicacy directory:
Rename the old version. We’ll use the move command to rename, rather than the rename command, because rename is not installed in some types of Linux–but everyone should have move installed. As root or using sudo:
mv duplicacy duplicacy.old
Also using a mv command, move your new version into your duplicacy directory. If all your other running programs are saved, you can reboot your machine. The new version should autostart, just like the old version did. You can confirm the running version number at the bottom of the web dashboard.
If things did not go as expected, don’t reply here! Submit a support request.