Hi Gebbel,
if you have booked with Ryanair, it will be very difficult and costly to make any change. Ryanair changed a flight on me, I was invited to either apply for a full refund or apply for a travel credit and there the fun started. Eventhough I applied only for a travel credit on 1 leg and intended to use that travel credit to apply against a new booking for the return flight, they claim I ticket a box which applied for a travel credit for both the outward and return flight. The only way to appeal that was to write by fax to the customer service department. I wrote on the 8th may and to-date they have not responded. (various calls to their customer service dept at Eur 1 per minute plus copious reminders by fax, no response !). Now, I have been able to resolve it by completely changing my holiday arrangements and with the help of the people we rent the accomodation from who have been extremely flexible (in sharp contrast to Ryanair).
Now Michael O'Leary will tell you that 67 million passengers in Europe love his service. Well, I never was a fan anyway, but he now has at least 2 customers less. At this stage, if Ryanair is the only option left, I will not travel.
Hope you've booked with Anbody Else But Ryanair.