Disable the real-time protection in Windows Defender.
You can do this from the Settings tab in Windows Defender, which you can access from the scan using Windows Defender prior to updating to Windows 8.1.
The next screen will give you a brief preview of what new features Windows 8.1 provides. Now just wait while the update is downloaded and installed.
If the highlighted "Svchost.exe" process has high CPU usage in combination with high memory usage (say Nothing worked. Important: This 15-step tutorial will walk you through the entire process of updating your copy of Windows 8 to Windows 8.1, which takes about 30 to 45 minutes.If you have a previous version of Windows (like 7, Vista, etc.) and want to upgrade to Windows 8.1, you'll need to purchase a copy of Windows 8.1 (Windows 8 with the 8.1 update already included).However, you can continue to use your system while this download it taking place.If you have the option of a wired Ethernet connection rather than Wi-Fi, I'd recommend using it to provide a much more reliable connection for faster download speeds and to reduce the risk of getting disconnected during the install.