How do you change the order number in Shopify?

Shopify order numbers themselves cannot be changed, however, you can add a prefix or a suffix to your order numbers so that they are more personalised to your store. For example, you can add a prefix such as '#ST1001' or a suffix such as '1001-A'.

Do this in 'Settings', 'General', 'Standards and Formats' then 'Edit Order ID Format'.