changing your mail addy on the site and on impulse is not the same.
about impulse customer account you should contact stardock support by sending a mail to firstname.lastname@example.org and referring with a link to this post.
About the site itself, go here: http://www.wincustomize.com/myaccount.aspx then on orange tabs click on stardock account.
When you're there enter your current email addy and password to access the settings.
Then on tab click on logon info and update your email.