For security and system integrity reasons, it is not possible to change the email address of an existing user.
If you would like to use a new email address (e.g. due to a name change or a new email account), please create a new user in the User management section with the desired email address and appropriate access rights (more info on user rights here) - and add them to your account. You can then remove the old user if needed.
Please note: Only administrators can add new users to an account.
You can find a detailed guide on how to add a new user here.