Download the demo from http://vst.saschart.com plugin page. Follow the installation instructions on the link from plugin page and try it out.
If the plugin meets your requirements, pay for the product on KVR Marketplace.
Click on Get Unlock Key from plugin interface. Login/register to your account at http://vst.saschart.com/members/index.php.
If the payment has been made, you will find in this account the unlock key to convert demo version to commercial version. Not any additional download required.
