You must have an "Unlimited Plus" license with an active Software Maintenance Agreement (SMA) to be able to manage your instance of VM Backup through the CP.
SMA Renewals as well as upgrades to the "Unlimited Plus" edition license will work in the exact same way as current upgrades from one edition to another and can be done through our customer portal: https://portal.altaro.com
For more information on our pricing please see: http://www.altaro.com/vm-backup/pricing.php
If the above requirements are not met, you will be shown the below error message in the CP: