We had this happen for our flight. Air Tran changed our departure from Orlando from 10 PM non stop to 6 PM with a 3 hour layover. We would have been leaving several hours earlier and getting into Philly later. I flipped on them... I have been planning this trip for a year, and I had every last minute planned out. First, as above, ask what they are willing to do for you. They may offer a voucher (Air Tran did, I didn't want it.) They offered a flight the next day, but I couldn't get them to pay for our hotel ahead of time, they wanted to reimburse us for an extra night AFTER we got back, and that was not acceptable to me. (Hey, call me what you want, some say it rhymes with witch, but they changed MY plans.PLUS, I know they could have gotten the room paid for, they have a very close relationship with WDW TC) So, I checked for other flights on other airlines, and got a 9 PM flight on US Air. I demanded, and got, a full refund from AirTran. If they will not refund you, this is a guaranteed dispute for every credit card company in the US (hubby has been at Bank of America in disputes for 17 years) as they are not delivering what you purchased. Threaten them with that if they balk at a refund. You do not have to accept their changes...just stand firm and know what you want. Good luck, and please post the results.
Oh, and PS, the back of the plane is NOT cool for motion sickness. Spent an entire flight to Houston in the back of the plane PRAYING for the plane to stop spinning. Doesn't happen in the front or middle.