https://www.techradar.com/news/you-can-now-download-windows-10-redstone-5-iso-files-for-a-clean-install

If you fancy testing out a future version of Windows 10, Microsoft has now made it possible to perform a fresh install of Windows 10 Redstone 5 by officially releasing the ISO files for the upcoming major update.

ISO files are essentially disc images that enable you to burn bootable CD or DVDs – or create bootable USB sticks – so that you can perform a fresh install of Windows 10 Redstone 5.