Finding out which version of .Net Framework you have installed

From: http://msdn.microsoft.com/en-us/library/hh925568(v=vs.110).aspx

To find .NET Framework versions by viewing the registry (.NET Framework 1-4)

1. On the Start menu, choose Run.
2. In the Open box, enter regedit.exe.
   You must have administrative credentials to run regedit.exe.
3. In the Registry Editor, open the following subkey:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP
   The installed versions are listed under the NDP subkey. The version number is stored in the Version entry. For the .NET Framework 4 the Version entry is under the Client or Full subkey (under NDP), or under both subkeys.

To find .NET Framework versions by viewing the registry (.NET Framework 4.5 and later)

1. On the Start menu, choose Run.
2. In the Open box, enter regedit.exe.
   You must have administrative credentials to run regedit.exe.
3. In the Registry Editor, open the following subkey:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full

Note
If the Full subkey is not present, then you do not have a the .NET Framework 4.5 or later installed.

Check for a DWORD value named Release. The existence of the Release DWORD indicates that the .NET Framework 4.5 or newer has been installed on that computer.

The value of the Release DWORD indicates which version of the .NET Framework is installed.

Value of the Release DWORD	Version
378389	.NET Framework 4.5
378675	.NET Framework 4.5.1 installed with Windows 8.1
378758	.NET Framework 4.5.1 installed on Windows 8, Windows 7 SP1, or Windows Vista SP2
379893	.NET Framework 4.5.2