If you wanted to edit the shipping in PowerStore, you will need to update the Shipping Server Behavior that is on the confirm page. If you open the confirm page, then open the Server Behaviors Panel (Window -> Server Behaviors). From there you could the different shipping server behaviors that are used in PowerStore, and based on the shipping provider you selected you can update the shipping server behavior.
note: with updating the shipping server behavior you might loose the ability of making changes in the admin section.