Recently I needed to change a flight to Liverpool from a Tuesday to a Wednesday. I contacted Aer Lingus 3 weeks beforehand and was informed that as per their policy it would be €100 per person to change. We payed for another flight which worked out cheaper. It also made me feel better, as I didn't pay for the exchange and they couldn't sell off our initial flight bookings again. Lose Lose situation but.......Expect to pay at least €100