Welcome. If you have a Windows 7 computer and it is telling you that you need to upgrade it to Windows 10 I think I can help you upgrade it without paying a cent. . Despite what you may have been told you definitely do NOT need to buy a copy of Windows 10. So without worrying about how much Windows 10 is to buy or where you actually buy it from let me show you how you can upgrade your own machine without forking out more of your hard earned money.
To download Windows 10. All you go need to do is go to Microsoft's official site and download it. This is a totally legal copy of Windows 10 provided by Microsoft themselves. You need have no concerns about this being counterfeit or pirated software.
I should point out is that you need a 16GB USB stick. You will use this in the first step to create a copy of Windows 10 so you can upgrade your computer so that means it is essential. Other than that you only need a decent internet connection as the download is quiet large at approx 4GB, Follow all the steps on the Microsoft site and you can't go wrong. If you do run into any trouble then leave a comment below. Good luck !