Generally, it'd be through either the 'Quit Tones' option in the member panel - it should be on the services page where'd you normally level up/master decks - or the information change page. I believe you should, once removed, be able to rejoin using the same information/e-mail as before, but if there's any problems with that, we can figure a fix out.

I can go ahead and remove you manually, though, so you don't have go through the extra steps!