Need help with .NET Framework

Hi everybody,
I want to uninstall all verzije.NET Framework and reinstall . How does it work? Where I find them because I am smudge and I have not them in the Add / Remove.
In C: Windows / Microsoft.NET / Framework... have... v.1.1.4322, v.2.0.50727.3053, v.3.0, v.3.5
Some applications are demanding version 2.0 and will not be installed because the scanning say that these versions is not on my computer.
Everything I tried using Microsoft's instructions but failed to solve the problem. I have even deepened as I took off a Microsoft program to uninstall. NET framework, and in fact I did not deinstalisao but I just deleted their names and the other installations.
When I tried to make a new installation .NET Framework 2.0 always get the answer that the installation dont do it should be respected hierachy.Consequently, layperson, I think would be best to uninstall everything and reinstall everything .... your suggestions to sequence of instruction.
The Microsoft error report writes that can not install the update ( This update true that we very large prbleme during boot):
Microsoft.NEWT_Framework_2.0_KB974417_20091110_222805406.html ....\PC Healt\ErrorRep\QSignoff\25AF6E3.cab
Microsoft.NEWT_Framework_2.0_KB958481_20091109_223320656.html " " " \44D2F5.cab
It is important to me to know ... .... step by step how to do it.
Excuse me for my bad english.Thank you for your trouble

Use .NET Removal Tool to remove all .NET versions, then install 3.5 full package which includes v 2.0,3.0,3.5.

Removal tool: http://blogs.msdn.com/astebner/pages/8904493.aspx
.NET 3.5 SP1 full package : http://download.microsoft.com/download/2/0.../dotnetfx35.exe

Thanks @Romeo29