Thanks for writing in!
I tried checking the website URL hat's listed in your licence manager but it's asking for username and password. You should not get notice to purchase additional X Theme licence. Are you getting the message in website or Apex Forum?
On staging website you need to first validate X Theme. Once validation is completed, you can proceed to update X and Cornerstone either Automatically or manually. I suggest you to take a look at following resource:
In case you still have problems validating and updating theme, please share login details in secure note for us to take a closer look at the setup.