You have the possibility until the shipping of the goods to cancel individual items of an order.
Go to Shop-Backend in the corresponding order details and select the item "ID Tags". Here you can see all ID tags of this order.
You can use the "Options" button on the right hand side of the the desired ID tag you can select the option "cancel". After the ID tag was canceled, the order overview is updated directly and the price of the order is automatically recalculated.
Important: This action can only be executed as long as the order has not been shipped.