Your main email address -- the one you'll use to log into the system -- is the one you signed up with. If you want to change which address you use for that:
- Click or tap Account Settings in the upper right.
- Select the Edit Account Info button.
- Under Contact Info, select "Edit contact info" or click Contact Info on the left side menu.
- Next to the main email, select Edit.
- Enter the new email address.
- If the address is already associated with your account, you're done!
- If the address is one you haven't added previously, log into that email account, where you should have a message from "firstname.lastname@example.org" containing a verification code. Paste the verification code into the field provided and click Verify.
This new main email address will now be the address you use when you log in.