How can I disconnect my YouTube account from TubeUpload?

There should be no need to do this, but if you do wish to, you can revoke access by logging in to the relevant Google/YouTube account and going to https://security.google.com/settings/security/permissions?pli=1. If you can't see it there, go to https://www.youtube.com/account_advanced and click the "Authorized sites to your Google Account" link.