It is a good idea that the license is automatically transferred during an uninstallation of an application. The user could then use the Serial Number on a new computer again.
If you use an own installer, add in the uninstall script the following command:
Player APP Name.exe -transfer (Player APP Name is the name of your application)
The license transfer is done without displaying any screens.
If you want to display screens use
Player APP Name.exe -transfer -dialog
•The transfer is only done when the product was already activated
•More details about the license transfer functionality