All new license purchases include one year of Software Update Service (SUS) that entitles you to version upgrade licenses throughout the life of your SUS. You will be required to renew this annually to continue the service.
NOTE: Plesk 8.4 for Linux/Unix license purchases are only for use on Plesk (8.0 - 8.4) for Linux/Unix servers and are not able to be used or transferred to Plesk for Windows servers.