If you call CRO and have them check by your name, do not tell them you already have a ressie before they check, some of them get all confused and try to pull it up, which is unnecessary. If, however, you find that you have a code, find out what it is and then call your TA and she can have them honor it for you. I don't think you can change it if you have booked with a TA. Or maybe your TA will call for you to see if you have any codes??