Three separate logins exist and they are frequently confused.
THE THREE
Client Area: billing, invoices, domains and tickets. Logs in with your email address.
cPanel: files, email accounts and databases. Logs in with a cPanel username. Your website admin, such as WordPress: content and plugins. Its own separate login.
Changing one does not change the others.
REACHING CPANEL WITHOUT THE PASSWORD
Client Area > Services > My Services > click the package > "Login to cPanel". This signs you in directly, with no password needed. This is the easiest route and works even if the domain is not yet resolving.
FINDING OR RESETTING THE CPANEL PASSWORD
The username is in your welcome email and on the service page. To set a new password, use the Change Password option on the service page in the Client Area.
Note that this may also reset associated database passwords depending on the options, so check before applying it to a live site.
DIRECT ACCESS
yourdomain.com/cpanel once the domain resolves, or the server hostname from your welcome email before it does.