I think this is a good question. But this is not a big problem "Change Yahoo Mail Password". But many users are facing the problem while changing the password. But you don't have to worried about it. Just follow the given steps.
Steps to Change Yahoo Mail Password:
From a desktop:
Sign in to the Yahoo Account security page.
Click Change password.
Enter a new password.
From Yahoo mobile apps:
Tap the Menu icon Image of the side menu icon..
If using the Yahoo Mail app, tap Manage Accounts.
Tap Account info.
Tap Security settings.
Enter your security code.
Tap Change password.
Tap I would rather change my password.
Enter the new password and its confirmation and tap Continue.