Thanks for the replies guys. I sent an email to the travel agency last night and this is the response I got;

''After contacting with the town office of Lufthansa in Athens, advised us that they cannot change the surname of the passenger. The only possibility that you have is to cancel the ticket under the wrong name and buy a new one. According to the airline fare rules the fare and fuel surcharge are non-refundable.''

They also said I could reclaim €76 in taxes but that I would have to pay €20 in fees.

I've spoken to two Lufthansa employees in Dublin and they both quoted their airline policy which is not to allow name changes on tickets. I'll ring again and this time ask to speak with a manager. I think that's the last option available to me. The tickets were booked on a visa debit card so I don't think I have any comeback there.