You cannot change the email address on an existing account directly. Your account, cards, and verified profile are tied to the email you use to log in.
If you want to use a different email, you can switch to another account (see How do I switch Accounts?). This opens a separate account and does not move your cards or balance to it.
If you can no longer log in with your email, see I Can't Access My Email Anymore. What Can I Do?