Are you using Windows 10 on a OEM computer as I'm going to post tomorrow a Windows 10 Pro OEM Edition on the newest build from MS
On my version you will need to do a new install, But you could try and just do the upgrade as see - But like I said it's a OEM Edition and will lock to your info, So if you need to reinstall it will be very easy
If it's not OEM, Please let me know and I will find a way