How to Change a Yahoo Messenger Password While Logged In
You can change your Yahoo! Messenger password while logged into the program. However, if your Yahoo! Messenger is set up to sign in automatically, you will have to change the password on the log in screen the next time you log into Yahoo! Messenger after the change. When you change your password, be sure to change it to something hard to guess. Adding a couple numbers usually improves the security of the password. Your messenger password is the same as your Yahoo! email password.
Open the Yahoo! Messenger program on your computer. Log in.
Click on "Messenger" on the tool bar of the friends list. Select "My Account Info" from the dropdown menu.
A webpage opens up asking for your current password. Type in your password and continue.
Scroll down until you see "Change your password." Click it. Type your current password and new password in the boxes.