$ VBoxManage modifyhd "/Users/USERNAME/VirtualBox VMs/Ubuntu server (remote)/Ubuntu.vdi" --resize 32000
Result:
0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%
Command:
$ VBoxManage showhdinfo VirtualBox\ VMs/Ubuntu\ server\ \(remote\)/Ubuntu.vdi
Result:
UUID: 008958e8-xxxx-xxxx-xxxxx-489529b51863
Parent UUID: base
State: locked write
Type: normal (base)
Location: /Users/USERNAME/VirtualBox VMs/Ubuntu server (remote)/Ubuntu.vdi
Storage format: VDI
Format variant: dynamic default
Capacity: 32000 MBytes
Size on disk: 7426 MBytes
Encryption: disabled
In use by VMs: Ubuntu server (remote) (UUID: f483a9a3-xxxx-xxxx-xxxxx-3326b709f4b4)