Originally Posted by
MIAFlyer
Usually there is no fee to change to a higher cabin of service. The term you need to use is "up-faring my current ticket". I have done exactly your scenario multiple times on both domestic U.S. and international (Latin America) itineraries, purchased through our corporate Concur/BCD travel booking engine.
Good Luck!
I have upfared on 4 different flights this year and was charged the third party fee each time. My tickets were booked via my corporate Concur booking engine.