You can rebook online if:
You booked your ticket online at www.austrian.com
Your fare conditions allow rebooking.
The new flight has an Austrian Airlines flight number.
What booking details can I change?
The flight time
The booking class of your ticket.
What are the deadlines for rebooking?
Fully flexible ticket: up to 3 hours before departure.
All other tickets: up to 24 hours before departure.