First of all, it is necessary to understand that no account can be registered with an email that already exists in another account. So, what may be happening is that you may have created an account at some point in the past with the email you wish to update in your current account.
In this case, the ideal is to access this account and delete it, if possible, or even change it's email address so that your current email can be registered in your new account.
Therefore, if you do not remember the password for this old account, click here to understand how to recover the password.
When recovering it, click here to know more about how to delete the account and to be able to register this email in your current account.
When you delete this old account that had the email address you want to register with your current account, you'll be able change the email normally.
In case you really can't proceed with these fixes, and need our team's help, please contact us requesting the deletion of the account with the destination e-mail, preferably using that email address!