The download in your free account at my.tracking202.com is always the latest release of Prosper202 ClickServer, for new users and existing users alike. There is no upgrade fee. The steps are on the Installation page.
A fresh install asks for your Prosper202 Customer API key during setup. Step 0 explains what the key is for and where to find it.
ClickServer can show a notice under the header when a newer release is out, with a 1-Click Upgrade button that uses your Customer API key. That notice doesn’t offer 1.9.78: to move to 1.9.78, download it from your account and upgrade by hand. Back up your database and your 202-config.php file before you upgrade; see Upgrading Prosper202. What changed in each release is in the release notes.
Support is separate from the download. If you need help, support plans are at my.tracking202.com.