You also use your reseller account username and password (WHM) to log into cPanel. Therefore you can change the account password from cPanel by following the instructions in this article: How to change the password of my Linux hosting account (cPanel)?
Follow the steps below to change the password of your Linux reseller account. You can follow the same steps to change the password for any other account you host.
1. Go to "WHM" > "Acccount Functions".
2. Then click on "Password Modification".
2. Select your primary domain, enter the new password in the field "New Password", confirm the password then click on the "Change Password" button.
A password generator is available on the page. It will help you choose a strong password.
If you forgot the password to access the WHM, you can reset it from the cPanel login page > "Reset Password".