On that page there are download links. You can choose to download the steam version which appears to come in 3 parts. There is an all in one torrent version you can download with a torrent client.
There is also a base game version that you can download in multiple parts.
All of the direct downloads use free services, but most will limit how much you can download in a given day so it would probably be best to download parts from different services.
You will almost certainly require a zip or rar program as well to extract the files.
I havent downloaded the game so I cant be more specific.