You can change your Yahoo mail password by following the steps below:
1.Click on https://login.yahoo.com/
2.Enter your username and password appropriately and click "Sign In"
3.Under "Sign-in and Security", click "Change your password"
4.Type your new password in the "New password" field, then type it again in the "Confirm new password" field.
6.You'll get a message confirming that you successfully changed your password.
7.Again click "Continue"
Now your password is successfully changed. Henceforth, you will need to login with your new password.
This link can be helpful:
Hope this will help you.