Sorry for the late response. Instead of roughly describing what I did I preffered to take the time to go through the process step by step as it may help better.
First of all I made a backup of my configuration as described by BK Hobby in his YT video “openHAB 2 Basics - Upgrade procedure | Common issues solutions and tips!”
https://www.youtube.com/watch?v=JIhxs3xFj0I
I startet the openHabian configuration tool
sudo openhabian-config
Then I ran an update on the configuration tool itself - just to be sure.
01 | Update
After completion, I could run the upgrade to the latest test version (milestone) 2.4.0 M5
40 | openHAB related
| openHAB testing
After the update I had to remove and discover all my Z-Wave devices.
Additionally I had to adjust all their channels as for some reason the Home ID of my Z-Stick changed from some 8-digit ID to some awfully long thing.
2.3.0: zwave:device:XXXXXXXX:nodeY:channel_Z
2.4.0-M5: zwave:device:FFFFFFFF-FFFF-FFFF-XXXX-XXXXXXXXXXXX:nodeY:channel_Z
The FFFFFF… is from the actual Home ID, the XXX… seem to be some hex digits.
So that was quite a surprise (as I have to admit not to have read the M5 change log) but after adopting the changes in my items-files it was okay.
Hope that was some helpful info for you.
Edit: you should really spend the time to read ZWave Binding Update info prior to he update.