Please copy the serial number and start the LiveZilla Server Admin application (you should find an icon on your desktop). Select Server Configuration and follow the wizard until your reach the server configuration form. Switch to the Licensing / Premium tab and
click the Activate button next to the regarding License / Premium Option and enter / paste the serial number.
If you receive an error while trying to activate, there are three possible causes which are:
You have no (unrestricted) access to the internet or you are behind a proxy. Please make sure that you have access to the internet (HTTP / Port 80) and/or configure your proxy in the regarding LiveZilla Server Profile (LiveZilla Server Admin -> Server Configuration -> Edit -> Proxy Information) or try it from another computer/network.