How do I transfer a license from one domain to another?

Start by moving the entire site (files and database).

When the site is running on the new domain, open the extra in the manager to trigger a license check. For example if you use Redactor open the resource edit page, or for Commerce open its dashboard.

Shortly after you'll receive an email about an invalid license. Follow the link in the email (or find the site in the list, typically at the top) and follow the instructions there to transfer the license. 

After you've corrected the license, a new license key is automatically downloaded to your site. No further action is needed.