Change Account Password in WHM
From Lunarpages Web Hosting Wiki
This is how you would change an account password in Web Host Manager (WHM). Occasionally, a user may forget his password and not be able to access his cPanel control panel. You can create a new one for him in WHM.
The first thing you would need to do is login to WHM. From the front page, click on "Account Functions" and then "Password Modification". This will lead you to the Passwords page inside of WHM for your account.
Enter the new password into the empty text box. It should be 6-8 charecters and should not include the user name for the account. Next, click on the domain for which you would like to create the new password. The last step would be to hit the "Change Password" button.
Now you can advise the user of the account that the password for cPanel and FTP has been changed.