Flights that get cheaper

Booked my next flight 2 days ago and got S class both ways.

Just checked again today and now there is K availible on the outbound!

£300 cheaper, anyone changed an S to a K before? Is this possible?

Thanks

[preiffer]

I think it's only possible through a cancel and rebook (or change of flight dates for later on). In which case - unless you can use the S later in the year, it might cost you more than you'll save.