Yes, you can modify your ticket for up to 48 hours at no cost. On the confirmation email, there is a link, that allows ticket change up to 48 hours before the scheduled departure time. By clicking on the link, you will be brought to the online self-service portal (the same as our booking system). Continuing through the purchase flow, you will select your desired trip and then proceed to checkout. Changing the ticket is super easy and you will get a new ticket once confirmed.
If you would like to change it over the phone it is possible, yet it comes with a $10 fee.