You can change volume size only by increasing it. Volumes can be extended for both running (online resizing) and stopped (offline resizing) virtual machines. Online volume resizing allows users to avoid downtime and enables scaling VM storage capacity on the fly without service interruption.
Limitations
You cannot shrink volumes.
During volume resizing, the file system inside the guest OS is not extended.
If you revert a volume to a snapshot that was taken before the volume extension, the new volume size will be retained.