You need to request before. Otherwise you will get an error when you log in. That's what happened to us as I forgot to do that first. Once I noticed I went in and had the new key within a few minutes but I would request it first.

they do not speak of a new license key.. but a new version of smartermail

just look up your license key you use now for v12 and use it in the upgraded version

good luck with the upgrade