Thanks for asking.
If you are working on a complete new project, then only you need to purchase new licence. For updating existing website there is no need to purchase additional licence. Please do following to update:
- Under X > Validation click on Revoke validation.
2. After that using existing licence, please validate the website again.
3. Then follow our theme update guide to update X Theme and Cornerstone.
In case you face issues with validation, please take a look at following article for some solution.
If you still have problems kindly get back to us with the result of the steps above and URL/User/Pass of your WordPress dashboard using the Secure Note functionality of the post to follow up the case.