After resist for long time expecting for bug fixing from Microsoft, last year finally I went from my great Windows 7 Ultimate to Windows 10 in my home made (then) five years old workstation... despite the free offer for the upgradetechnically was dued, I had no diffcults to upgrade it straightly from their site... free of charge, of course!
Microsoft has all interest to turn everybody to the last Windows release so if you have a regular license from previous OS I think you will have no difficulties to get free upgrade. Why do not test?