Myself and my partner were seated separately so looked at the cost of changing. I thought we'd only have to pay for a single change, but all seats beside both of us were showing as unavailable. To sit together we'd have had to make two separate changes, cheapest option was 24 euros.
We ended up not bothering and just switching seats after the plane had boarded. There quite a few empty seats so it was easily done. I might be tempted to pay 6 euros but not 24 for a short flight.