A number of ways to determine the version of S4S you have installed.
1. File Information: If you have access to the server where the connector is installed, you can browse to the bin directory of the website and view the properties of the FuseIT.Sitecore.Salesforce DLL.
2. Status Page: In S4S release 1.6.13297.1 (Sitecore 6) and 1.7.13344.1 (Sitecore7) or later, we introduced a status page at http://yoursite/sitecore/admin/S4Sstatus.aspx. This will give you the version number, as well as lots of other information about your site.
3. Sitecore Logs: In the Sitecore log files, we write out the version number when the connector is first loaded. You can search for the text "FuseIT.Sitecore.Salesforce.Licensing" which appears as follows: