Lost that DVD? That USB key? Misplaced your ISO? Microsoft has you covered! Below are the official links to download media directly from the source.
Windows 10 (Media Creation Tool) – https://www.microsoft.com/en-us/software-download/windows10
NOTE: If you’re looking to upgrade an existing system, use the media creation tool. It will intelligently download the necessary bits and walk you through the Windows 10 upgrade process.
Windows 10 (ISO) – https://www.microsoft.com/en-us/software-download/windows10ISO