Mar 19, 2016 - 02:06 PM
Your ticket from FCO > Roma Tiburtina is a regional train ticket, it can be used for another date and/or time as long as it is within 2 months of the purchase date. It can only be used on another regional train, and the route cannot be changed. You would select the new time when you have the ticket printed.
The ticket from Roma Tiburtina > Firenze SMN is a Super Economy fare, unfortunately per Trenitalia's fare rules listed online and on your confirmation email, this fare cannot be changed, cancelled, or refunded.