You can make changes from:
<For smartphone>
After logging in, select Top page > Hamburger icon (mark with three lines) at the upper right hand corner of the screen > Login information > Change your login e-mail address
<For PC>
After logging in, select Top page > Login information at the top of the screen > Change your login e-mail address
Note that if you change your login e-mail address, a change confirmation e-mail will be sent to your new e-mail address.
Click the link in the e-mail message to complete the e-mail address change.
Note that if 30 minutes or more pass without any click action, the changes made to the login e-mail address will be canceled.
In such cases, please restart your registration process from the beginning.
To change your e-mail address, note that if your e-mail address is set as the notification destination for the two-factor authentication during login, disable two-factor authentication, and then set up a new e-mail address.
<Related questions>
Q. How do I disable the two-factor authentication setting?
Q. How do I set the two-factor authentication?