Originally Posted by
KLflyerRalph
I think you can't do that unless you have a fully flexible fare?
Not full fare, but a B fare will allow you to upgrade, even if it's Delta operated.
And yes, usually buying such fare is more expensive than it's worth. But it's bought by my employer. And by contract, they will only buy economy tickets (even when it's actually cheaper to get a business ticket). So I usually upgrade my trips with my FB points.