When you use the free upgrade (from Win 7 or Win 8.1 only), the upgrade will be the same version as you currently have. You don't get to choose which version.
Also, you can't do a clean install of Win 10, initially. You have to upgrade. You can do a clean install after the upgrade, using the product code of the version that was upgraded.
The ten forums have lots of info on Win 10
www.tenforums.com