Hi shegga,
Login to our site with the same username and password while you have purchase the theme and download the latest version of the theme.
If you have still one year subscription you will have access to the download the update file. After doing this just activate any of the theme eg:- twenty fourteen and then if you haven’t change any code then you are safe to update and delete the interface theme. Add the new theme from dashboard -> appearance -> themes
Thank you!