To upload files in the document directory (or) your hosting space, you need to upload the files via FTP protocol. FTP protocol will be available via FTP clients like FileZilla, cuteFTP, etc.
Filezilla is the easiest way of upload/download the files to your local machine. Kindly follow the link below to download the FTP client - FileZilla.
Then you can upload the files via FTP client. Kindly have the configuration steps for filezilla.
Port number: 21
Username: cPanel username
Password: cPanel password