In order to upload files, you will need to have an FTP client such as CuteFTP, LeapFTP and CyD FTP. To login to your account using an FTP client, you will need to set up a new connection and use the following logins:
Username: ftp.yoursite.com
Password: your Cpanel password
Once you log in, go to the /public_html/ directory and start uploading!
Alternatively, you can use the File Manager option within your Cpanel, it works exactly like an FTP client.