Have you switched to Windows 10 yet? BGR has an article up on How to stop Windows 10 spying on you. This article is well worth a read as it is good to know just how to stop Microsoft gathering all your information.
Also, a personal story. I updated a Windows 8.1 Laptop to Windows 10. The upgrade took overnight and took a while but went as expected. Then I had the bright idea to use the “reset to factory defaults” option to refresh the machine and get a clean windows install. This went along until it rebooted at the end and the device was bricked, unable to find the boot device. If this happens to you, you can solve the problem by creating a boot DVD or USB stick with the Microsoft download tool and do a clean install of the OS. The trick is when it asks for a device key (Windows 8/8.1 has them in the BIOS) to skip these steps. By the time it finishes installing it sorts itself out and you get an activated Windows 10 install. Just be sure not to try and install Pro if your old Windows 8 was Home and vice versa.