Gruppo Ferrovie dello Stato

If you are a customer registered at the Trenitalia website, you can change date and time of your tickets with simultaneous place booking (Eurostar Italia, Eurostar Italia Fast, Eurostar City Italia, Eurostar Italia Alta Velocità, Eurostar Italia Alta Velocità Fast, Intercity, couchettes, WL, Excelsior, Excelsior E4,  IC, ICN and  Espressi only with the ticketless procedure ).
You can use the reservation change online just in case you travel with one or more train of the same category (for example with two AV trains from Turin to Milan and from Milan to Naples) and the reservation change must regard the same route, same fare and same number of passengers.

You must use the Booking Code (PNR) and Booking Change Code (CP), which are printed on the tickets (see example in Italian only) or were sent by e-mail when buying.  

You can carry out the Reservation Change online (operative every day, 24 hours) until the booked train's departure, by directly entering the codes:

Please Note

If you choose a  ticketless solution you can make the booking change only with the ticketless procedure (you cannot pick up the coupon of the new booking at the self-service points).
Should the booking change instead refer to a ticket that has already been picked up, you must print the booking-change coupon and show it to the on-board inspection personnel together with the original ticket. 
You can pick up the new booking at the self-service machines in the stations (typing in the PNR and CP codes) or, if this is not possible, at the station ticket desks, as well as at the issuing agency or the Eurostar Clubs (for holders of Executive Cartaviaggio, Flexi, AV and first-class AV Fast tickets).