If you click on your avatar up in the top right and choose “Change options”, you should see the option to change your email, as per this screenshot (admittedly I haven’t followed through and tried to actually change mine) -
The odd thing is when I go to that option my current screen name is in the Email box and not my "to-be-changed" email. Chrome also wants to change my login credentials. I didn't do it yet.
Hmm, when I go there that box is blank, ready for me to enter a new email address (I’m using Safari on an ipad). I’m wondering if that’s just Chrome being “helpful” and trying to auto fill what it thinks the form wants?