I need to add/change the data on the credit card receipt sent to customers by email.  The current message reads:

"Dear _______ ,    This is a confirmation of an online transaction placed with ______.     The Sale transaction totaled $____ and will be processed to your account.   Order Number : ____   Approval Code : ____"

Not sure where that date on "Order Number" is coming from but the customer is demanding to reference their PO number on that receipt!  Can you please direct me on how to do that?  Thanks