From PowerShell, you can do it like this:
$swis = Connect-Swis
$uri = "swis://./orion/Orion.Nodes/NodeID=1/Volumes/VolumeID=2"
Remove-SwisObject $swis $uri
To get the Uri for a volume, you can use a query:
$uri = Get-SwisData $swis "SELECT Uri FROM Orion.Volumes WHERE criteria"
If you'd like to use a language other than PowerShell, you can do this through SOAP. Let me know if you'd like more details.