I booked my flight on Southwest and it is operated by AirTran, I went to change the time and It won't let me, so are we not allowed to change our flights if they are operated by AirTran
I had a flight scheduled on Air tran and didn't have any problems switching to a SWA flight a few weeks ago. I would suggest calling their Customer Service number --they have always been very helpful in solving any issues I might be having.