I run octoprint on an old laptop and I now get the error: 'You are still running Python 2' where some of you are probably familiar with. I clicked on the link 'Migrate to Python 3' to read how I can migrate it but I don't understand it. I'm a total noob when it comes down to things like this and therefore I would appreciate some help.
Do I need to completely remove my octoprint (dont know how) and then set it up again from scratch but with version 3 of python? and make a backup or smth?
Unfortunately, it's not possible to run the automatic upgrade script on Windows, as you probably found out and is why you are asking this question.
You would need to remove the virtual environment you created for OctoPrint, download & install Python 3 and then reinstall OctoPrint. The configuration would be saved, but plugins would need to be redownloaded afterwards, even though their config is also saved.
Refer back to the install guide, specifically the section labelled 'Installing Python and OctoPrint':