How to remove your Tumblr account
It should be easy to delete your account here. Also see http://www.tumblr.com/docs/en/account
Direct removal link: http://www.tumblr.com/account/delete
Helpful Trick: Removing online data
Helpful Trick: Remove third-party logins
If you signed up for Tumblr using a third-party login such as Facebook or Twitter, you probably want to revoke all access from Tumblr. Click here to find out how.