You can upload files to your site through the File Manager within your cPanel interface. Click on File Manager, and then scroll down to the directory you wish to put the files in.
You can also use an external FTP program to upload files. You'll probably want to create a FTP account to do this. Go to the FTP Manager and create an account with access to your
public_html directory, then use your external FTP program to upload your site's files to that directory.