I actually read all the small prints and call the MPO to enquire the other day. They said all bookable upgrade must be requested via the website. Exact same thought - if only it's another airline (website) then I am not too worry but since it's CX... The agent said of course if any tech issues then they could do the upgrade request via the phone.

Anyways, for bookable upgrade - the request must be made 15 days prior to departure. The agent told me usually within 24 hours the upgrade would be granted/tickets converted to A class providing that there's still A fare selling on that flight. I also read the small print saying that because it is an upgraded ticket, online check in will not be available and can only be done at the airport counter. I am not too fuss about this however I just find it so odd that you can't check in online because of that (then again it's CX IT we're talking about!). I will be using one of the bookable upgrades very soon once I have finalised my JFK itinerary so I shall report back in a week or two.