You are absolutely able to change the email and password you use for your account.
First, you can go to the My Account tab on your top navigation bar in your ThankView account. Click Settings in order to see details about your account.
On the right of the first section of the page you can update your email or password by clicking on "Update name and email" or "Change Password."
If you have any problems with changing your email or password, you can email firstname.lastname@example.org for any additional help.