To Cancel a shipment, you must access the Shipment's Booking Details page.  

From the Main Dashboard, find the shipment you wish to Cancel and select the ‘EDIT’ button on the far right side.  

This takes you to the shipment's Booking Details page.  Scroll halfway down the page on the right, click ‘Cancel Booking’ Button.

This IMMEDIATELY CANCELS your shipment.

Please Note: 
The air waybill number used for this booking will be lost and cannot be reused.
If you accidentally Cancel a shipment, you cannot recover the shipment and must create a New Shipment.
To find Canceled Shipments, the Shipments Tab on the Left Sidebar will allow the user to review all Canceled shipments.