Originally Posted by abuswiss

Both offered at checkin and on-board (as long as EK ticket, non-EK ticket could be problematic). 2 weeks ago on IAD-DXB, purchased miles at the gate and transfered some from Amex, both happened instantly and the gate agent processed J-F upgrade. Also on-board may be more expensive and may potentially cause catering problem closer to departure you do it (depending on route).