I queried this in a previous thread, as I had just suddenly noticed these fees for the first time when making a booking. £150pp for flight changes seems to be the norm - "money" and "old rope" comes to mind if all you're trying to do is upgrade.

As it turns out, I wasn't charged, but I was just trying to UUA, which couldn't be done online anyway, and the consensus here was that it shouldn't attract a change fee for that reason.

Something to watch out for anyway...