If you no longer need a particular work item queue, then you can delete it.
For more details about this operation, see
Selectingand clearing rows. If needed, first search the queues. Searching for queues is similar to searching for users. For more details about this, see
Searching Users. It lists the queues satisfying your search criteria.
A queue cannot be deleted even if the workitem available to the queue members is reassigned to another user. This is because the queue is the actual owner of the workstep instance. Only when the workstep instance is completed ,then you can delete the queue.
Business Process Server deletes the selected work item queue and it is removed from the list.