Updated March 18th, 2015. When you register a username account at WordPress.com the email address you provide becomes your unique identifier. You can register as many blogs as you wish and provided you are logged in, when registering all the blogs you register will be registered under that username account and the associated email address.
Deleting a Blog
To delete a free hosted WordPress.COM blog you must be logged in under the exact same username account and associated email address that registered it. To delete a WordPress.com blog, go to Tools -> Delete Site in your Dashboard. You will undertake a step by step process wherein three warnings will be issued letting you know the result will be permanently deleting the blog address ie. URL and all content. An email confirmation will be sent with a verification link in it and when you click that link the blog address ie. URL will be deleted forevermore. Note that deleted blog addresses ie. URLs are not recycled at WordPress.com.
Alternatively, to change blog visibility to private go to > Settings > Reading scroll to Blog Visibility and choose option 3 . See the privacy setting guide.
Deleting Blog Content
If you decide you no longer want your WordPress.com blog content but do want to retain the blog address ie. the URL, you can easily delete all blog content by yourself.
If your content is a large collection then you can post to the WordPress.com support forum and Staff will delete all the content for you.
IMPORTANT NOTE: Deleting blogs and/or blog content does not remove any indexed items from the SERPs (search engine page results). Google and Bing only clear their caches of deleted indexed content that produces a 404 (page not found) every 3 – 6 months. See here to completely remove an entire page from Google search results.
Deleting a Username Account
All you were required to provide to register an account here was an email address that can be replaced at any time. Any personal information that you voluntarily posted can also be removed at any time.
Although username accounts are not deleted at WordPress.com, so you cannot be impersonated and have your reputation affected by anyone registering the same username in the future, there are steps you can take that amount to removing all personal information and result in leaving only a throwaway email address behind. This is what you can do to deactivate your username account:
1. You can go to My Account-> Edit Profile and remove all data except the account name and an email address. Create a throwaway email address and change the account email to that throwaway address. This only leaves the username behind.
2. To unsubscribe from email sent to you from WordPress.com, go here http://wordpress.com/#!/read/subsettings/ and click on “Block all email updates from blogs you’re following on WordPress.com”.
3. To ensure the account is locked up tightly, visit this site, generate a password of 15-20 characters, and change the account password to it:
4. To hide your Gravatar profile, login and on the bottom right hand corner of your Gravatar profile page you will find a “hide” button visible only to you that you can click. Please read “How to Make Your Gravatar Profile Private” section of the Gravatar help page.