If you run into a message telling you that you need to upgrade to add more items, you may have one in to one of a few issues:
You ran into your limit and deleted items, but you need to reset your account to register the change.
Close and reopen the app OR uninstall and re-install if you are sure you are not at your limit and you need to clear the upgrade message. Contact support if you continue to run into an issue.
You received a shared account from someone else, and your limit needs to be adjusted.