The free upgrade offer countdown:
You still have a few days time to decide. You can test Windows 10 without installing it, fast and easy with a free 90 day trial Windows 10 pre-installed on a virtual hard disk which you can mount on your system for native VHD boot. Do it, test Windows 10, delete the downloaded VHD file if not happy and your PC has not the slightest trace you ever tested Windows 10.
If you have Windows 7:
If you have Windows 8 or 8.1:
Tutorials on our sister forums: