What exercise? The upgrade guide tells you exactly how to remove what leftover files. You could copy and paste the rm commands mindlessly, not that I would sugg

What exercise? The upgrade guide tells you exactly how to remove what leftover files. You could copy and paste the rm commands mindlessly, not that I would suggest doing anything mindlessly. If you're using the official OpenBSD packages, they would be linked to the correct libraries for that release, so there's no need to worry about linking to the wrong libraries. If you're compiling your own packages, you should be aware of anything you've done with any libraries that would require you pay any particular attention necessary to files being removed. Otherwise, it's not anything you would need be concerned about as a user. Where do you get the idea that a clean install is the correct way to upgrade? Considering how conservative OpenBSD is, it would not provide an upgrade process if it wasn't something that was very well supported.