Originally Posted by
AKC6
In their world, they changed the equipment and the carrier, not the flight; they are still transporting you from point to point. However, as
jrl767 points out, you can change your flight for free--with a human being on the phone. If you see another PBI-MSN itin you like, ask for it.
You don't mention how soon the flights are. There may be another schedule change between now and then, and you could wait for a better itin, but that's a two-edged sword. The nicer seats get taken, or you may be put back on mainline, but an Airbus

, and then you're out of luck.
The 717 to CRJ-900 is a change from DL mainline to DL Connection, so in the DOT world it is a change of carrier and the OP is entitled to a free change or refund to the original form of payment.