From https://meta.stackexchange.com/questions/5999/how-can-i-delete-my-account 

> The [Help Center explains][1] that there are two cases:
> 
> **If your account has interacted with the site** by voting or posting, go to the [Contact Support page][2.5] and fill out the form. One of
> the items in the topics drop-down list is for account deletion.
> 
> You can also get to that page via the "contact us" section on the site
> footer. Please note that account deletion is not instant. It might
> take several days for your request to be processed. 
> 
> Due to [a known
> issue](https://meta.stackexchange.com/questions/155901/further-anonymize-deleted-accounts-by-changing-the-username-prior-to-deletion),
> you might want to change your username before deleting the account.
> 
> **If your account has never voted or posted a question or answer more than once**, you should see a self-delete option on your user page
> next to the *edit* link:
> 
> ![screenshot][3]
> 
> Either of these procedures cover deleting your account on **one
> specific site**.
> 
> **Content you've posted on the site** [is owned by you but licensed to Stack
> Exchange](https://meta.stackexchange.com/questions/18221/who-owns-the-content-i-post),
> and you therefore cannot request that it be deleted with your account.
> 
> Also of note, we automatically cull old inactive accounts as
> documented on the blog:
> 
>  - [When is an Account Abandoned?][4]

  [2.5]: http://stackoverflow.com/contact


  [1]: http://stackoverflow.com/help/deleting-account
  [2]: https://meta.stackexchange.com/questions/81343/how-to-sync-my-profile-on-all-stackexchange-sites
  [3]: https://i.sstatic.net/dlqrE.png
  [4]: http://blog.stackoverflow.com/2009/02/when-is-an-account-abandoned/