On your settings page there is an “Alternate Email Addresses” section. Find the email you’d like to unlink and simply click “unlink”.
Once unlinked, this email will be its own independent, empty account. If you’d like to login to that new account (to delete it, manage it separately, etc) you will first need to set a password for it, which you can do via the forgot password page. You can then login using the email address and new password for that account.