The .NET Framework Cleanup Tool is a free portable tool which quickly removes the version of the .NET Framework you select from a PC.
This is generally a dangerous thing to do and likely to break a host of applications and cause more harm than good, but if you're sure .NET is corrupted on your PC, and repairs, reinstalls and every other troubleshooting step has failed then it just might save your life.
If you're determined to go ahead, it's all very easy. Download the cleanup tool, unzip and launch it (the program is portable, no installation is required). Then choose the version of the .NET Framework that you'd like to remove, click Cleanup Now and it'll be properly removed for you.
The .NET Framework Cleanup Tool supports the following Framework products:
.NET Framework – All Versions
.NET Framework – All Versions (Tablet PC and Media Center)
.NET Framework – All Versions (Windows Server 2003)
.NET Framework – All Versions (Windows Vista and Windows Server 2008)
.NET Framework – All Versions (Windows 7)
.NET Framework 1.0
.NET Framework 1.1
.NET Framework 2.0
.NET Framework 3.0
.NET Framework 3.5
.NET Framework 4
.NET Framework 4.5
.NET Framework 4.5.1
.NET Framework 4.5.2
.NET Framework 4.6
.NET Framework 4.6.1
.NET Framework 4.6.2
While this can be a life-saver, the author says that the removal process will strip out shared Registry keys required by other Framework versions, so you'll need to be prepared to reinstall all of these (not just the one you're removing). Check the tool's home page for more details.