One can delete a Yahoo account by visiting the "Terminating Your Yahoo Account" page. Deleting a Yahoo email account will erase everything associated with it.
Once an account is deleted, the user will no longer have access to their Yahoo.com email, Yahoo messenger profile, Flickr account or personalized settings on their Yahoo homepage.
When attempting to delete a Yahoo email account, the password will be needed in order to complete the process. It may take up to 90 days for the account is removed. This precaution was set as a measure to prevent malicious account closures. After the account is officially deleted, the Yahoo username will be available for selection by other users.