There is a .Net framework "cleanup" tool here but read carefully before using it. click here
NOTE: This tool is designed as a last resort for cases where install, uninstall, repair or patch installation did not succeed for unusual reasons. It is not a substitute for the standard uninstall procedure.
You should try the steps listed in this blog post before using this cleanup tool.
This cleanup tool will delete shared files and registry keys used by other versions of the .NET Framework.
If you run the cleanup tool, you will need to perform a repair/re-install for all other versions of the .NET Framework that are on your computer or they will not work correctly afterwards.