To delete an entire device, open the Manage tab in the SpiderOak One or Groups application. Next, select the device you would like to remove and then click the Remove button. When prompted if you would like to remove the device, choose yes. This will remove the device and those files that are associated with it and no other device. For more details, see What Files Are Deleted When You Delete a Device.

It is not possible to restore a deleted device or its files, so make sure that this is what you want.