If you are making changes in the given time frame then you don't have to pay any Virgin Australia Change Flight Fee. Flight Cancellation fee depends on the time of changes, class of tickets, or type of changes made. if you are making changes offline like by visiting at the airport or through call then you would have to pay a service fee of around 50 to 100USD.

https://airlinespolicy.com/flight-change-policy/virgin-australia-flight-change-policy/