On my last DTW-AMS flight, they changed equipment from 333 to 332 several days before the flight, moving me from 10B to 29A. I just happened to recheck my itinerary, saw it and called them to change to to other seats, but there were no seats available other than center section non-aisle seats, so I was stuck with a window seat. Then they changed it back to a 333 two days later. I was checking often for any seats opening up, so I caught it, but 10B was already assigned to someone else. Fortunately 10H was still open (had been filled before these changes), so I took that. I was very annoyed that they didn't put me back in my original seat, but whoever originally had 10H ended up in worse shape.