I'm trying to update Octoprint from 1.4 to 1.7.3 but it keeps failing at the same point either in normal as in safe mode.
What did you already try to solve it?
Update Octopi with apt, updating PIP since I heard there were some issues there too. Update in safe mode and only Octoprint itself but it keeps failing.
Have you tried running in safe mode?
Yes
Did running in safe mode solve the problem?
Nope
Systeminfo Bundle
You can download this in OctoPrint's System Information dialog ... no bundle, no support!)
1.4.0 doesn't seem to have that yet I added an octoprint and plugin.software log down below
It is quite pointless uploading your files to a website that only allows you to download them once. Just upload the log files to the forums, no need for external services.
Anyway, to come back to your issue, OctoPi 0.15 is too old to be supported on newer versions of OctoPrint. I would suggest creating a backup of your current OctoPrint settings & plugins from the built in backup & restore, then re-flash the latest version of OctoPi (0.18), from OctoPrint.org - Download & Setup OctoPrint.
That will additionally migrate your install to Python 3, as we've been trying to get people to do for the last 18 months and will be a hard requirement for OctoPrint 1.8.0, which is currently in the second release candidate.
If anyone else would like to look at the logs, I've reuploaded them here since they were deleted after downloading from the links above: