It looks like you want to use Stardock's page here:
https://www.stardock.com/support/
Top of the page is "Retrieve Serial Number / Latest Build" which looks like what you're after. Looks like you'll have to go through an extra step if you're email has changed since you bought it and you haven't already changed it with them.
Do uninstall the version you've got installed now before you load the next one.
(As frustrated posters go, you're not sounding so bad. 
)
