In general, there are two ways for changing the domain of your license:
1.) Plugin settings
The recommended way would look as follows:
- Deactivate your current site
- Remove your license key, click “Activate License” and afterward uninstall the plugin
- Install the plugin on your new site and activate it by entering your license key again
2.) Account page
In case you don't have access to your old site anymore, don't worry.
Log into your account page, click on “Licenses” and “Manage Sites”.
Here you can remove your old domain. Afterward, add the new domain to the license (in the best case directly via plugin settings).