Your Yahoo! password always applies to your entire Yahoo! account. This means that it is valid not only for Yahoo! Mail, but also for Yahoo! Messenger, the Yahoo! Music Engine, My Yahoo!, Yahoo! Finance, and all of Yahoo!'s other personalized services. If someone breaks into any of these accounts, you’ll want to change your password.
Here’s how to change your password from Yahoo! Mail:

1. Log in to your Yahoo! Mail account.
   
   
2. Click your name (in this example, User) in the Hi, User greeting at the top-left of the page. From the menu that appears, select Account Info. A new browser screen appears asking you to verify your password.
   
   
3. Type your password into the box and click Sign In. The Account Information page appears.
   
   
4. From the Account Info menu, select Change Password.
   
   
5. Type your Current Password in the first box.
6. Type your New Password in the second box.
   
   Note: Passwords are case sensitive and must be at least six characters long.
7. Confirm your New Password by typing it again in the third box.
8. Click Save. Your password has been changed.

Note: Your Yahoo! password always applies to your entire Yahoo! account. This means that it is valid not only for Yahoo! Mail, but also for Yahoo! Messenger, the Yahoo! Music Engine, My Yahoo!, Yahoo! Finance, and all of Yahoo!'s other personalized services.
For more information on Yahoo! IDs and passwords, please visit the Sign-in and Registration help page.