Change sign-in e-mail?

And no, I don’t mean the e-mail that all the notifications gets sent to, I mean the one I use to sign it. Thing is; I changed the e-mail associated with my Gamertag, and it would be useful if I could use the new e-mail here too.

I wouldn’t mind knowing as well, because I will probably be doing this in the future too.

I would goto the MS passport homepage and change your details there, then everything you sign in using the passport should reflect that change.