Both live in your account settings once you're signed in.
Changing your email address
Update it in settings. If you signed up with Google or Apple, your sign-in stays tied to that provider, so changing a contact address there doesn't change how you log in.
Changing your password
Also in settings. This applies to accounts created with an email address. Google and Apple accounts don't have a MagicShot password, because authentication happens with the provider.
If you can't get in to change it
Settings are behind the login, so you need access first. See trouble signing in.
