In the last 24 hours I've updated 10 x Win 7 Pro PCs (with assorted hardware) to Win 10 Pro.
None of these updates have been automatic.
I've had best results with the Windows Update Tool.
I usually got "something happened" errors if I tried to update directly, but creating a USB (once only) and running setup.exe has worked every time.
Usually the software does not ask for your Windows 7 key, but keep it handy just in case ....
Win 10 activation is automatic after the update.
Love Windows 10