Almost all server and account settings can be modified through cPanel's Web Host Manager - WHM.
Most hosting companies using cPanel do not allow access to WHM for accounts hosted on a shared server. WHM access is often given only to accounts hosted on dedicated solutions.
To change passwords from WHM, you should first log in by going to:
The root password can be changed from Server Configuration > Change Root Password.
The password for a specific account can be changed from Account Functions > Password Modification.
Select the account whose password you want to change and enter the new one.