how do I change my email address

You can change the email used for your Apple ID at appleid.apple.com. In the account section, choose Edit, then choose Change Apple ID. If your Apple ID is an email address ending in @mac.com, @me.com, or @icloud.com, you can change your Apple ID to a different email address, but you can't create a new @icloud.com email address.

Change your Apple ID - Apple Support

You can change the email used for auto-fill in Safari and in apps by changing the information in your card in the Contacts app. Add your contact info on iPhone - Apple Support