We provide an option to upgrade but not downgrade virtual servers.
This is because we can only automatically scale up partitions of virtual machines, but not scale them down as we risk destroying all of the data stored on the virtual server due to damaging the partitions.
The only way to normally downgrade a generic virtual server's disk space is by manually downsizing the partitions then scaling down the size of the virtual disk, but we cannot do this as only the client knows how the disk is being used, and what files are where and we do not want to risk destroying the client's data. Due to this, we only allow upgrading of VPS and not downgrading.
If you'd like to downgrade your virtual server, purchase a smaller virtual server and transfer your data to that, then request a cancellation for your old one.