Changed our 50% 2 4 1 booking today from the late SFO > LHR to the earlier flight. Called You First. No problem at all and all done in about 2 mins. I had checked availablity beforehand so knew it was available. 3 seats in First, a refund of 77gbp per person so 222gbp back !! No 30gbp charge either. Happy with the flights, very happy with the cash back !