SDC question from newbie

Hi Guys,

I have never used SDC before, and as recent PM, I just wanted to confirm a couple of things:
1. What time before departure should I call Delta to ask for change?
2. We have already been upgraded (RU) on the flight that I am looking to change. What happens to the upgrades if RU is still available on the new flight? Is it automatic? What if RU is not available?

Thanks for helping out newbie PM. :confused: