Found the relevant part, basically there is a cost of 30 euro to change the flight time for one way.
-----------------------------------------------------------------
How much will a flight date/time or route change cost?
Flight dates, times and routes are changeable subject to availability, upon payment of the current change fee - Click here for details. Plus in each case any difference in cost between the original total price paid and the lowest total price available at the time the change is if applicable. If the total price is lower on the new flight, no refund will be made.
If the total price is lower on the new flight, no refund will be made.