I called and gave it a try and was told I would have to apply for another card and I don't want to open another account. They did offer me a $1,500 CLI for not being able to do it.
Where you trying to convert to or from a co-branded card. I have read that many of the stores prohibit this.
I asked the rep if I can get my nonrewards card converted into a rewards card and she said I have to apply for another card.