Your Osclass installation can't be auto-upgraded. Files and folders need to be writable. You can apply write permissions via SSH with the command "chmod -R a+w *" (without quotes) or via an FTP client, it depends on the program so we can not provide more information. You can also upgrade Osclass by downloading the upgrade package, unzipping it and replacing the files on your server with the ones in the package.

OK so it says you cant upgrade from admin. Great.  Whats the point of having an upgrade tab?

Then it says download the "upgrade package"?  Where the heck is that?  Presumably an "upgrade" package is different from a fresh install package.

Lets just say I have an upgrade package and I overwrite all of my current directories and files.  Then what? Wait for the upgrade fairy to come visit and wave wand?

What release had the major changes to database structure?

This is totally crazy.

You need to write an sql script to execute in phpMyadmin that will update 3.9 database to conform with the structure of 3.9+ database.  Then we can simply export the changed 3.9 database and import it into 3.9+ database.

@pixelpadre2
Simply said all your folders in osclass must be writtable.
Best way to achieve that is setting chmod on all folders (recursively) to 0755.
Different hostings provides different way to achieve that.
If you find such folder that does not have chmod on 0755, feel free to post it there as other people may have similar issue.
I would first check ox-content folder (uploads, downloads especially)
You may check upgrade-func.php to see whole history of sql changes.

You havent answered the question about when the table structure changed.

Nor have you presented a querry to change the old database to conform to the new database.

@pixelpadre2
No query, no table structure.
If you follow upgrade instructions, your questions are irrelevant as osclass takes care about all the changed.
If you do not follow instructions, do it as you like.

Why did you not contribute all new changes on github where is 3.9 version?
This is right now "official" repo...
It is a good idea to see new changes/amendments  have been done.

@Ivanko
There is no official repo at all. Official is that one that you call like that.
I've been checking github at start and there are few issues:
- there was no activity for more than year (yes there were some license updates etc, ..), no real update has been released after 3.9
- I've checked v5 branch recently and could actually just see that in defines, version has been changed from 4.0.0 to 5.0.0, but there was no 4.0.0 released, so it's just reaction someone is working on osclass and quickly get highest number available. But we might go to osclass 2020.3 and release quarterly updates, this number would not be overcome any time soon... but it does not make sense
- many updates has been ignored on github with no explanation (you may simply find some guys complaining their work has been completely ignored)
- most of changes in v3.9 were moving files in oc-includes directory, that's same for v5.0. A lot of updates but actually nothing important, class changes, renaming, reorganization, restructuralization, license changes etc... so log of changes is full, but it has no impact. It does not make sense to change structure of osclass files in each upgrade and then see people complaining their plugin or theme is not working because file does not exists or class name has changed and just say, right you are using old product, update it - but noone will do that, most of free plugins and themes are just created and left for community. Or tell developer, but developer will ignore that as well - use some old version of osclass would be answer
- considering all of these, using repo you are referring would be same blocker for updates as osclass market has been, where update could be available to end-user in several months and not immediatelly it is made.

Reason why we did not put all the updates into new repo on github is simple - at this moment it does not make sense and there is no benefit out of that.

@Ivanko
There is no official repo at all. Official is that one that you call like that.
I've been checking github at start and there are few issues:
- there was no activity for more than year (yes there were some license updates etc, ..), no real update has been released after 3.9
- I've checked v5 branch recently and could actually just see that in defines, version has been changed from 4.0.0 to 5.0.0, but there was no 4.0.0 released, so it's just reaction someone is working on osclass and quickly get highest number available. But we might go to osclass 2020.3 and release quarterly updates, this number would not be overcome any time soon... but it does not make sense
- many updates has been ignored on github with no explanation (you may simply find some guys complaining their work has been completely ignored)
- most of changes in v3.9 were moving files in oc-includes directory, that's same for v5.0. A lot of updates but actually nothing important, class changes, renaming, reorganization, restructuralization, license changes etc... so log of changes is full, but it has no impact. It does not make sense to change structure of osclass files in each upgrade and then see people complaining their plugin or theme is not working because file does not exists or class name has changed and just say, right you are using old product, update it - but noone will do that, most of free plugins and themes are just created and left for community. Or tell developer, but developer will ignore that as well - use some old version of osclass would be answer
- considering all of these, using repo you are referring would be same blocker for updates as osclass market has been, where update could be available to end-user in several months and not immediatelly it is made.

Reason why we did not put all the updates into new repo on github is simple - at this moment it does not make sense and there is no benefit out of that.

The benefit very big, everyone can see changes in code.
I believe you are working more then guys produced 3.9 and 5.0.
If you put you version on github some people sure will assist in coding,report bugs,etc.
Please consider it.
With you updates and other people helps you may take a lead)

@Ivanko
You know that sometimes review & test commit from someone else may take more time than do it by yourself.
In that case only logical solution is to accept commits without testing or do not accept any commits at all.