We have tickets DEN-IAH that cost us about $420 each. However, we will need to change this to DEN-DFW and the cost of that right now is about $260.

So when we make the change, I assume we'll have to pay the $100 change fee per ticket, then do we get a credit for the fare difference of $160 each? Or do we lose that fare difference? If we get the credit, do we have to pay another $100 change fee to apply it toward a new ticket?

Thanks!