Originally Posted by Londonflyer
Experts may disagree, but you might be able to use the value of the tickets you have bought towards the cost of the new ticket - in otherwards just pay the difference, rather than dumping the original reservation. I guess a ticket agent at BA might be the best person to ask.
It is certainly worth asking. Some fares (even cheapo fares) are upgradeable whilst others are not. Most are not but you never know.