To change your email address:
Go to your Profile settings (click your avatar → Profile).
Click on your current email address and type the new one.
Click Save.
A verification email will be sent to your new address. The change does not take effect until you click the verification link in that email. Until then, you can still log in with your old email address.
If you do not receive the verification email within a few minutes, check your spam folder. You can also resend it from the Profile page.