In light of the recent massive data spill after Yahoo's violation but also according to Yahoo our morning publication which states that the company allowed the automated scanning of incoming emails to US intelligence services, there are many who are considering closing their accounts. 
To close your Yahoo account, visit this page, and sign in with your credentials.
Follow the instructions that appear on screen. Θα χρειαστεί να εισαγάγετε ξανά τον κωδικό πρόσβασής σας, αλλά και ένα CAPTCHA before clicking on "End this account".
If you've done everything right, you'll receive a confirmation that the account has actually been deleted.
You should know that if you close your account, all your Yahoo services will cease to work, and your personal settings will be deleted.
Of course before deleting your account you can download your contacts as a .csv file for importtreatment them to the new account you will create on the service you choose.
https://help.yahoo.com/kb/SLN22580.html
