You can use "Control Panel" in Windows 8 to enable the .NET Framework 3.5. To do that, please follow these steps:

(1) On the "Start" screen type "turn on windows features", click "Settings", and then click "Turn Windows features on or off."

(2) Under "Turn Windows features on or off", click .Net Framework 3.5. Note: wizard will search for required files and then prompt you to download the files from Windows Update.

(3) Click Download files from Windows Update.

(4) Click Finish.