If a customer email needs to be updated then follow these steps:
1. Log in to the dashboard and go to customers and edit the email address for the customer. Once you update the new email address, click on save and go back to Dashboard Home.
2. Click on Orders and go to the specific order id of that customer and click on Edit Order.
3. In the first step of Edit an Order screen, search for the customer with the new email id and select that customer. This will re-populate the customer billing details but will take into account the new email address. Click on Next and go through the steps of editing the order.
4. At the final step of Edit an Order screen, you will see the new email id in the Finalize Payment Section of the order (Top right corner of the screen). You can email the invoice to this new email address by click on the check box that says "Email Invoice to Customer? "
5. Now this order id will have the new email address of the customer and any new orders from this customer will also reflect the new email address.