I have a Lenovo laptop that had Windows 8 preinstalled on it, and I upgraded it to Windows 10 while it was free for Windows 7/8 users. I would like to format the laptop to Windows 10 so I can sell it, but I can't find a way to reinstall Windows 10 without any sort of product key. Is it possible to format my laptop to Windows 10 without a product key?
This is not related to the question this is marked a duplicate of because that question is about making a clean install of Windows 10 using the free upgrade. I am asking if, after the free upgrade, if I can clear all the files/programs/settings/etc..