My host is telling me I have too many files on my server and so I need to clear some off. Do I need to keep the old upgrade files such as “upgrade_2.1.2_professional-2.1.3_professional” in the “public_html/var/upgrade” directory? I'm on version 2.2.1
How many times have you needed to access your old upgrade files since you first began saving them? 
Seeing that I haven't upgraded in more than a year . . . I wasn't sure if they were needed as I'm setup to upgrade now with each new release.
Knox,
Personally, after I complete a successful upgrade & have migrated all customizations, I only retain the upgrade files from the most recent upgrade on the server, just until the next release becomes available.
You could retain the last two updates if you wanted to, however, more than this and you end up with a zillion MB's of redundent dunnage of which you will most likely never need.
My theory is that if I discover a hidden problem down the road, I won't be attempting to repair the problem by reverting to some older version, I will be comparing file or DB diffs to a fresh vanilla install of the same version I am currently running.
I also download our “entire” Cs-Cart store directory and database to my local PC just before performing an automated upgrade, I find this to be the best “just in case” fall back solution.
I'm not sure actually. I recently ran the upgrade for version 2.2.1. The upgrade was successful and all was good…Once I removed all the prior upgrades from 2.x to 2.1x, I now get a “your trial license has expired” error message at times in the admin. If I restore the upgraded files back, it goes away.
I decided to ignore the popup error messages since host provider requested that I remove files on my account. Removing these upgrade files has saved approx. 32k files, which has made my site run much faster.