There are several ways to do so. You can either login to you billing control panel-->my hosting services-->(choose the hosting plan)-->login to my Cpanel.
The second way is to access via your website: www.yourwebsite.com/cpanel and enter your control panel login. THIS IS DIFFERENT FROM YOUR BILLING CONTROL PANEL CREDENTIALS.
the third way is to go to www.siteforbiz.com/cpanel and do it form there.