You can only delete a volume if it's no longer in use and no snapshots of it exist. In order to check if this is the case follow these steps:
- Log in to the Dashboard
- Click on the Storage tab and select Volume Store.
- Go to the Volume Snapshots tab and delete any snapshots of the volume first.
- Then go to the Volumes tab and check whether to see if it's in use.
- If so, click on the drop-down menu to the right of the 'edit volume' button and click on Manage Attachments
- Click on detach volume
If this is done the volume is no longer in use and you should be able to delete the volume
- Click on the drop-down menu again and select Delete Volume