Hey Linda!
Thanks for reaching out.
YES, The Events Calendar must be installed for Events Calendar Pro to work. The Events Calendar is not so much the “free version” of the calendar features—think of it like WordPress itself, a “core” (or, in your words, “base”) spine of functionality that our premium add-ons like Events Calendar Pro add on to.
Next, in terms of “safely updating,” updating is not dangerous to begin with. 🙂 You should be able to auto-update when the notice to do so arrives in your dashboard; if such a notice doesn’t arrive, or if you want to manually perform the update, then you can get the files to do so at any time from here → http://theeventscalendar.com/my-account/downloads
If you want to test an update’s efficacy on the staging area before the production area, that’s fine—simply DO NOT enter your license key on staging, only keep it on production. The lack of license will make no impact on functionality whatsoever.
Then, manually update the files on your staging site by going to the link I shared above to download the files. See how things behave, and if all is well, perform the same update tasks on your licensed production site.
I hope this information helps!
Sincerely,
George