Tom
Take a run through this:
Pay specific attention to the section on the Media Creation Tool OR Rufus - either will handle all the tasks to either get you a USB of the latest files Or an ISO file (My preference) directly from Microsoft.
And ensure that your machine is correct activated (assuming its all good since you updated overtop of Windows 7). Since you are installing to the same machine - a clean Win 10 install will activate automatically.
Let us know how it goes if/when you get around to it.
Cheers
VP