I want to delete older versions of unity, as each version is about 3 Gigs, and I almost always install the newest version, so I have dozens of them, but I am afraid if I do, none of my backed up projects will fire up if the older version is gone.
Is it possible I can delete the older Unity versions, and just upgrade my backup projects if necessary if the need arises? Or should I do what I am doing now, and upgrade all my back ups to the latest version?
This is possible. I’ve just replaced my computer and instead of installing all of my old versions of unity, I decided to just update all of my old projects to the same version of Unity 2019.2. So far it’s working out just fine. For any project in Unity hub, you can simply select a different Unity version for it to open in. Keep in mind: you can always convert a new project to work with a newer Unity version, but if you try to open the project in an earlier version of Unity than that could corrupt your project.
Also, keep in mind that upgrading projects can cause complications. Various code/ assets/ what-not in your old project may not be compatible with the new version and there could be lot’s of little things that you need to fix to get it to work. If you’re not using source control, make a backup copy of your project first, then attempt to adapt the project to the new Unity version. Don’t delete the older version of Unity or your backup project folder until you are satisfied that the converted project works properly in the new Unity version. On one or two occasions I’ve actually screwed-up projects trying to convert them and had to start-over. This was no problem, though because I still had the original project backed-up.
The most complicated thing is if you have content for an asset store tool that has since been converted to package manager. Things like TextMeshPro and Pro Builder each have special instructions for converting content from one version to another. It can be a bit complicated to follow though. Other things, like Unity post-processing, I just started from scratch and didn’t bother trying to convert…
You don’t have to update all your backups now. You can remove all your rarely used versions of Unity and reinstall them as the need arises. As already mentioned there can be complications when updating a project’s Unity version. Don’t do the upgrade on your only backup.