The current build of Stardock Central is inappropriately showing that some people can "update" their DesktopX install to DesktopX Professional 3.1. Please untick that box if you are using the updates window.
It's not going to harm anything if you don't (it'll say you've updated to DesktopX 3.1 Pro, but won't really download the files to do it, unless you have a registration for it), but I can see where it would cause some confusion.
We'll get that fixed in the next SDC update.
Unless you've purchased DesktopX Pro, you're not supposed to see it or be able to download it (which you shouldn't be able to).