You are purchasing a yearly license subscription which entitles you to free updates and priority support. Until cancelled your subscription will automatically renew at a 20% discount. You can cancel at any time and are free to continue using the Premium version you already have at the time the license expires.
A license is valid for 1 live website. If you want to use the plugin on multiple websites, you’ll need to purchase a Multi-site license, which can be used on unlimited websites. For development or staging websites no additional license is required.