You can call YouFirst 2-3 days prior to departure and ask them, one other hint is to check (usually appears 5 days prior departure) where the bassinet (COT) seats are , if those are on row 5 then it is NF , if in row 1 is OF.
As BusinessTraveller said, follow that link. Has plenty of information.
BA does not give any guarantee of getting new F; and not having God-like powers, it does take a considerable length of time to re-fit those of BA’s 100-strong 747/777 fleet which will be getting the new cabin.
About 50% of the 747 fleet have new F, and the proportion of new F in the 777 fleet is higher.