From what I understand, but can't verify as I have not tried it, if you are running Windows 7/8/8.1 and it has been properly licensed and activated, you can download the Windows 10 download tool
https://forums.windowscentral.com/e?...token=fydxllla and still upgrade to W10 for free.
Again, I have not tried it, this is just what I have read. Worst case, after upgrading it won't have a valid license and you could just wipe it and go back to 7/8/8.1.
I may try it this weekend. I have an older laptop that still has 8.1 on it. I didn't upgrade it to W10 for free because I couldn't find the power brick back when the free upgrades were officially offered. Anyhow, a couple of months ago the power brick turned up.