The free version is hosted in WordPress' repository so you may install there.
Go to your WordPress Dashboard -> Plugins -> Add New. And then enter "bsk" as keywords to search and you'll see the following screenshot.
Click the "Install" button beside "BSK Contact Form 7 Blacklist" and then it will be installed to your site automatically.
After several seconds the button will change to "Activate" and please remember to click "Activate" and then the plugin activated in your site.
Purchase Contact Form 7 Blacklist