Microsoft has recently announced the release of .NET Framework 4.5 Developer Preview. It is an update to .NET Framework 4. Since it is a developer preview, it may not be stable and should not be installed on production systems. You can download and install it on test systems for testing the new features included in the new version of .NET Framework.
.NET Framework Developer Preview is designed to run side by side with .NET Framework 3.5 or earlier version of the product but will replace .NET Framework 4. If you are installing it on Windows 7 or Windows Server 2008, you can also uninstall it and it will roll back to the earlier version .NET Framework 4.
According to Microsoft Download site:
The .NET Framework 4.5 Developer Preview includes updates to the common language runtime (CLR) and the .NET Framework class library, innovations in the Visual Basic and C# languages, enhancements in data access and web server scenarios, and improvements in extensibility, performance, reliability, and security.
Supported Operating Systems:
Windows 7, Windows Server 2008 R2
Windows 7 (x86 and x64)
Windows Server 2008 R2 (x64)
Windows Developer Preview (x86 and x64)
Windows Server Developer Preview (x64)
Minimum Hardware Requirements:
1 GHz or faster processor
512 MB of RAM
850 MB of available hard disk space (x86)
2 GB of available hard disk space (x64)
Update: .NET Framework 4.5 Final has been released. Please download and install .NET Framework 4.5 final instead of developer preview.