You can download the Windows 10 installation using the Media Creation Tool on the Offical Microsoft page:

 

https://www.microsoft.com/en-us/software-download/windows10ISO

 

If your current computer is not supporting the Media Creation Tool, you can use the ISO downloads on that page.

 

Please make sure that you use the option Windows 10 (this is for Windows 10 Home and Professional) not any other version or your key will not work.