Final answer:
To calculate the fare difference and exchange a flight itinerary, passengers should contact the airline directly via their website, customer service, or at the airport ticketing counter.
Step-by-step explanation:
If a passenger wants to change their flight itinerary, to calculate the fare difference and exchange the ticket, they need to contact the airline directly. This can be done through the airline's official website, customer service phone line, or at the ticketing counter at the airport. The process involves checking the existing reservation, determining the cost of the new itinerary, and then calculating any additional fare or fees required for the change. The airline's reservation system will have the most up-to-date pricing and policies to ensure the passenger pays the correct amount. Once the difference is paid, the ticket can be exchanged, and the new itinerary confirmed.