GWX Control Panel

GWX Control Panel is a free program that you can use to do the following on Windows 7 and Windows 8: Remove the "Get Windows 10" icon that appears in your notification area. Prevent your Windows Update control panel from upgrading your computer to Windows 10. Prevent your computer from secretly downloading Windows 10 installation files. Detect and remove the hidden Windows 10 installation files if they're already on your PC.

http://ultimateoutsider.com/downloads/

A portable version of the application is available.