Click the MySQL Databases link in the Databases module.
Scroll down to Current Users, select the user you want to change the password for and click the Change Password link.
Enter a new password in the Password field. Note: There is a 5 character minimum and a strength level of at least 65 for database passwords. To auto create a strong password, click the Password Generator button. A dialog box opens for additional options.
Click the Change Password button.
You'll see a confirmation message that the password change was successful.
Once you've changed the MySQL database password, be sure to change the password used in any of PHP or Perl scripts that access the database.