The easiest method to access your accounts cPanel is to first login to the client area here: https://support.hostrocket.com/clientarea.php
Once logged in select 'Services' -> 'My Services' -> 'Manage Product 'next to the account you are trying to access -> then under 'Actions' select 'Login to cPanel'
Your cPanel is also accessible via any of the following links:
Please note, you may see certificate warnings within your browser when accessing cPanel from any url's other than https://server-name.com:2083. This is because the SSL certificate is issued for the server's hostname, and your browser will issue a warning when connecting to that certificate using a url that does not match that exact hostname. To avoid those warnings, update any bookmarks to use the server name cPanel url.
The cPanel runs on port 2083, so if you are behind a firewall or proxy server, you might have trouble accessing your cPanel if that port is blocked. Unfortunately, there is no way around this and the only resolution is to talk to your Network Adminstration about opening up that port for you.
For further information, the cPanel documentation for logging in can be found here.