Just used my first Amex 2-4-1 over the weekend to get flights for my wife and I to New York for a milestone birthday. Wanted return First but was only able to get First out and CW return. As I have upper deck seats return I am not too bothered but was curious to know if First availability opens up can I upgrade the return leg? If so how, as MMB says I cant upgrade an Avios booking. Do I just call the Gold line?

Tried searching for an answer but nothing came up.