Its relatively simple, really. At the right side of your screen, in the presets download library,
there are a series of boxes containing menus and such. At the bottom of the row is a box titled Submit a FXpreset. Just click the button in that box, and you can upload your preset file for submission. It will probably be a few days or so until its posted, so just be patient. If for some reason it doesn't get approved, the team will send you an email explaining why.
I look forward to seeing what you have come up with.