If you want to know all the .Net Framework versions installed on your machine, download and then run the DotNetVersion.exe utility.
Download DotNetVersion (free)
After downloading DotNetVersion.exe, just run DotNetVersion.exe.
DotNetVersion will display a window similar to the following one:
The above result indicates that the machine has the following versions of the .Net Framework installed: 2.0, 3.0, 3.5, 4.0, 4.6 and 4.6.2