Change a Customer’s Ticket Type
If the ticket you want to change for your customer is the same price as the ticket your customer currently has, you will simply want to Void their original ticket and send them a Complimentary ticket for the new ticket type.
You can find instructions on how to Void a ticket here: http://www.sparxo.com/knowledge-base/voiding-or-refunding-tickets/
You can find instructions on how to send a Complimentary ticket here: http://www.sparxo.com/knowledge-base/import-guests/
If there is a price difference that the customer would need to pay to change their existing ticket to a new ticket, it is best practice to have the customer purchase the new ticket altogether. Request the customer notify you after they purchase the new ticket and then you should Refund and Void their old ticket.