Under the light of the recent massive data leak after the Yahoo breach but also according to the our morning publication which states that the company enabled automated scanning of incoming e-mails post officey in the American intelligence services, there are many who are thinking of closing their accounts.
To close your Yahoo account, visit this page, and sign in with your credentials.
Follow the instructions on the screen. You will need to re-enter your password and a CAPTCHA before doing so click in "Termination of this account".
If you've done everything right, you'll receive a confirmation that the account has actually been deleted.
You should be aware that if you close your account, all of your Yahoo services will stop working, and your personal settings will be deleted.
Of course before deleting your account you can download your contacts as archive .csv for importtreatment them to the new account you will create on the service you choose.
https://help.yahoo.com/kb/SLN22580.html