Once logged in, on the Services dropdown > click My Services. This will bring you to the Products & Services page, which will list the hosting packages tied to your billing account.
Locate the hosting package you would like to change the cPanel password for, and click the "Manage Product" button.
On the management page for the hosting package, there will be an Actions menu on the left side of the page, You will want to use "Change Password" option to reset the cPanel password.
There is also a "Login to cPanel" option which will log you directly into cPanel. Please note, if you do not know your old password, you will want to change it using the process above rather than attempting to change it in cPanel.