The Change Your Booking option on BA
.com is, for the moment at least, is somewhat feminine in its ways due its erratic and unpredictable responses.
If flying longhaul, then you can usually upgrade V, R, M and K fares , as well as the Y, B and H fares for £50 plus the difference to WT
+. If you do look at the upgrade then don't leave it to the last minute as there is a 21 day advance purchase requirement on the lowest WT
+ fares. Getting upgardes on the day is not a sure fire thing at all, particularly if departing from a UK airport. As your travel is not for 8 months, it is quite possible that, if you went searching for the lowest fare, you would have purchased an N class ticket which is completely non-changeable.
Anyway, as said before, the simplest way to check if your ticket can be changed is not to ask a bunch of plane spotters, but ask whoever you booked the ticket with. If you booked the ticket online, try and make a duplicate reservation and if you can still get quoted the same price check the fare rules to see if changes are permitted at all.