Can I change my email address?

Yes, and it is self-serve now: Settings → Your account, beside the password box. You type your new address, and a confirmation link is sent to it — your sign-in email changes only when that link is confirmed, so a typo cannot lock you out. Two things happen deliberately at the same time: your OLD address is emailed that a change was REQUESTED (not that it happened — if somebody else is doing this, you still have time to act), and the wording never reveals whether the new address already has an account, because that would be a way to test which emails are registered here.