Updating from the Core Hotspots version to the PRO is easy. Once you subscribe you'll get access to the PRO downloads. Just navigate to Downloads -> Official Downloads -> Hotspots, select the latest release and in the directory you should now see the PRO version as well. Download it and after that install it on your site. You don't need to uninstall the core version. Hotspots PRO will make anything necessary to properly update your Core installation.