Unfortunately, you aren't able to change the email address attached to your account though it's something we hope to be able to do in future.
If you would like to have a new email address attached to your account, the option we have is to delete the account associated with the email address so that you are able to start a new account. Please be aware that by doing this you will lose the data associated with the original account. In order to do this, please contact our support team (support@smilingmind.com.au) and ask that they delete the existing account.