How can I update to Windows 10?

My laptop came with Vista, but the day I bought it, I blew that away and installed XP-pro. When it crashed a while back, the guy who repaired it updated it to Windows 7 because XP support was going away. It was a properly licensed version - I get all updates, etc. The only thing I didn't get was the little icon that allowed update to Windows 10.
Attempts to upgrade to Windows 10 on-line require a license key. I don't have one, and the guy who installed Win 7 is no longer available.
Is there any way around this?
Thanks