You can update your email address by going to your account summary and clicking "Change your email".
For security reasons, you might be asked to re-login, then enter your new email address. You'll need to enter a valid email that isn't currently in use.
You will then need to verify your new account by clicking the link in the email that will be sent to your new address.
Once verified, you can login with your new email and your account and all prior orders will be associated with the new email address.