Best practice for upgrading a Unity project with Collab?

When upgrading a project to a higher Unity version:

What should the other team members do - first sync the project in the old Unity version and then import it into the new Unity version - or first open it in the new Unity version, basically upgrading it again and then syncing it?

Ideally, there would be an easy way to sync a project outside of Unity. Is there something like that?

 

I guess it's true ... don't use Collab, use git or something.