That's exactly what I was thinking for this old laptop, as I've already done it with the other one. Actually, I tried to upgrading for free when Win10 came out (failed), and I still have the link or whatever it is that's supposed to allow me to upgrade for free.
But I'll have to replace the drive.
I could pay for a Win10 license with the new drive. But still -- do you happen to know if it's possible to use my "free upgrade" in this situation?