Line items with the status of new, selector-ready, order-ready, or pending-order can be deleted. Be sure you want to delete the line item as there is no warning message and once deleted line items cannot be un-deleted.
If you created copies for your line items before activating the purchase order you will need to delete the items from the catalogue before deleting the Acquisitions line item. See Deleting Holdings
Delete line item
Line items with the status of On-order cannot be deleted - these must be cancelled. See Cancel Acq for details