Assuming you have already created and saved/sent an order, do the followig to edit that order:
1. Select your past orders and find the previous order you want to edit
2. Select the order you want to edit. click anywhere on the order bar except the forward/send button
3. Select 'edit' from the fly out options
4. Now you can search for new articles and add them to the order OR remove items from the order.
4b. To remove items from the order:
5. Save or send the revised order