How to know if .Net Framework 4.5 installed?

.NET 4.5 is not running side by side with .Net 4.0. It is a upgrade.
.NET 4.5 overwrites .NET 4. So all of files are in the same folder.

Following are the different version for .Net 4.0
4.0.30319.1 = .NET 4.0 RTM
4.0.30319.269 = most common .NET 4.0 version we're seeing in the data collected from our users
4.0.30319.544 = another .NET 4.0 version that a small portion of our users have installed
4.0.30319.17626 = .NET 4.5 RC
4.0.30319.17929 = .NET 4.5 RTM
4.0.30319.18010 = current version on my Windows 8 machine

So there are many ways to know if .Net 4.5 installed
1. By System.dll version number: 4.0.30319.17626 or greater
2. By Registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Client
3. By code

  public static bool IsNet45OrNewer()
  {
      // Class "ReflectionContext" exists from .NET 4.5 onwards.
      return Type.GetType("System.Reflection.ReflectionContext", false) != null;
  }