To change the email address associated with your Desmos account, go to teacher.desmos.com and make sure to sign in. Click on your username in the upper right hand corner of the site and select Account Settings.
You'll see an option to Delete your Desmos Account?. Click on the link and then select Send Delete Account Email. We will send an email to your current email address with a link to delete your account.
If you're still having trouble, please feel free to reach out to us at info[at]desmos.com.