Remove your tumblr account?

Remove Tumblr Account

Log in with your email address and password if prompted to do so. Click the title of the blog you want to delete at top of the Tumblr Dashboard, next to the Tumblr logo. If you cannot see your blog title, click the "My Blogs" button, which looks like a bulleted list, and select it from the list that appears.

Keep in mind that, once your tumblr account is deleted, there is no other way to reactivate it and your blogs urls may be used to create other blogs.
Steps to delete your tumblr:
1. Login to your tumblr account using your credentials.
2. Click the following direct link for your account management and you will be able to delete your account as well as your primary and secondary blogs.
Direct Link: http://www.tumblr.com/account/manage