The .NET Framework 4.5 replaces the .NET Framework 4. When you install the .NET Framework 4.5 on a system that has the .NET Framework 4 installed, the assemblies are replaced.
if you uninstalling the .NET Framework 4.5 also removes pre-existing .NET Framework 4 files. If you want to go back to the .NET Framework 4, you must reinstall it and any updates to it
Download .NET Framework 4.5 Offline Install
x86-based and x64-based computers. This is the recommended package for non-web deployment. This package does not support Itanium-based computers.
You can download dotNetFx45_Full_x86_x64.exe for offline installer (no need internet connection) or from microsoft download center for web intaller (need internet conection)
The .NET Framework 4.5 redistributable was updated on October 9, 2012 to correct an issue related to an improper timestamp on a digital certificate, which caused the digital signature on files produced and signed by Microsoft to expire prematurely.