The Microsoft .NET Framework 4.5.1 is a highly compatible, in-place update to the Microsoft .NET Framework 4 and the Microsoft .NET Framework 4.5. The offline package can be used in situations where the web installer cannot be used due to lack of internet connectivity.
This is an offline installer. There are separate installers for web and offline installation. If you intend to redistribute either of these installers in the setup for your own product or application, we recommend that you choose the web installer because it is smaller and typically downloads faster. You can download the web installer here.
Wherever possible, Microsoft recommends you use the Web Installer in lieu of the Offline Package for optimal efficiency and bandwidth requirements.
The offline package can be used in situations where the web installer cannot be used due to lack of internet connectivity. This package is larger than the web installer and does not include the language packs. You can download and install the language packs from here.
This version of the .NET Framework runs side-by-side with the .NET Framework 3.5 SP1 and earlier versions, but performs an in-place update for the .NET Framework 4 and the .NET Framework 4.5.