If you want to change the password for your email address, you can do so in your Webmail.

First, log into your Webmail by visiting yourdomain.com/webmail in your browser (substituting "yourdomain.com" for your primary domain name):

Now log into your Webmail, using your email address as the username and the password for that email address as the password (make sure that you do not use your cPanel username and password at the webmail link):

Once you have logged in, make sure that the proper email address is showing and then click on "Change Password":

On this screen you can change your account password.  Once you have put in the new password that you want to use, click on "Change Password":

Now your password has been changed.