You do not need to install .NET Framework on Windows 8, as it already includes version 1.0, 1.1, 2.0, 3.0, 4.0 and 4.5. If you want to install programs that require .NET Framework 2.0/3.0/3.5, press Windows + X. Then, click Programs and Features. Click "Turn windows features on or off". Tick .NET Framework 3.5 (Includes .NET 2.0 and 3.0). Click OK. Then download it from Windows Update. And let it install.