If you want to close your Yahoo! account, you can follow the steps on the Account Termination
You will be asked to sign in or to verify the password for the account you want to delete.
Note: Before deleting your account, please read the instructions on the Account Termination page carefully, as important information about your account is included. You can then confirm the deletion of your account.
Please complete the deletion process only if you are certain you want to remove your entire Yahoo! account and any features you have personalized within the account. After you delete your Yahoo! account, you can't reactivate it, although you can always sign up for a new account.
When you close your account, you lose access to your Yahoo! ID, Yahoo! Mail, and profile names. We will delete your account data and settings across the Yahoo! network. This means you will lose all of your content in:
Yahoo! Address Book
Any other area of Yahoo! that can only be accessed with your Yahoo! ID and password.
Deleting your Yahoo! account does not alter or delete your Yahoo! People Search listing. You must edit or delete this separately.
If you are subscribed to any premium services, we recommend that you cancel them before you delete your account. There is no guarantee that deleting your Yahoo! account will immediately cancel the billing for any premium services you are subscribed to. To cancel your current subscriptions, visit Yahoo! Billing Information for your account, click My Services, and then click the Cancel link for each subscription.
Using an older version of Internet Explorer or Firefox subjects your PC to more vulnerabilities, viruses and spyware. To ensure you're protected, we recommend downloading a Yahoo! optimized version of Internet Explorer 8 or Firefox today.