This page consists of screenshots from the Installation Screen in Captcha Bank WordPress Plugin.
This gives an idea about the Installation Process.
In order to install Standard Edition of Captcha Bank WordPress Plugin, you would need to download it from wordpress.org
If you are installing premium versions of the plugin, the first step is to download the plugin sent via a link in your email which you mentioned while purchasing the Captcha Bank. After downloading, you would need to upload and install the zip file to your wordpress.