Admin can edit the order for the customer's details and order items detail (require Plus version and only when the item is marked not paid).
You may use Order or Order (B-View) to open the order details.
Click on the 'Pencil' icon to open the order items editor.
You may change many of the aspect of the orders including:
i) Add more items (within the form's product) into the order.
ii) Add existing order item's quantity.
iii) Change the price of the product.
iv) Remove order item from the list
v) Change the Delivery Type Name & Price
vi) Add discount
Make sure you hit 'Save Changes' to save all the changes you made.