To change the email associated with your UXPressia account, simply go to your profile page, enter a new email, and hit SAVE CHANGES.
After that, you will need to confirm your new email by clicking the link inside an email that will be sent to you shortly.
If you can't find the confirmation email, be sure to check this article.
Keep in mind that you cannot use email addresses that are associated with existing UXPressia accounts. So if you have two accounts but want to keep only one with, let's say your corporate email, you can delete your other account copying or moving all the projects to your corporate account prior to deletion.