Customer details can either be edited from the NEW ORDER page or from the SEARCH page:
From the NEW ORDER page
Enter the customer's name into the Name field on the new order screen and select them from the results that appear.
Click the pencil icon that appears next to the customer details boxes.
Edit their details then press the Update button.
From the SEARCH page
Select Customers from Order Type drop down.
Enter customer name, email or phone.
Press the Search Button.
Edit Customer details that appear below and click the green Update button.