To change the email, you must be inside your Taxmania account on the desktop screen. In the User Account section, choose the Manage Account option and then type the email you wish to use in the two boxes under Change Email.
You can also change your email from your return screen where you will need to click on the account icon in the top right and select the one you wish to change. You will need to enter the email twice to ensure there are no errors. An email will be sent to confirm your account. You must go to it, select confirm account and you are done.