This video needs to and will be remade; at the moment it's done using an older version of the tool, on an earlier build of Windows 10. However, although both Windows and this tool have changed the process itself has remained the same. I thought it might help some of you guys, so I will embed it here.
Video shows how you can grab the ESD file even before the upgrade process starts. This is practical if you have no intention to wait through the whole upgrade process but want instead just make the ISO for a clean install.
If you do want to let Windows Update to upgrade your Windows 10 and only create the ISO for later use and Windows maintenance, use this link to see the video starting at the point where you already have secured the ESD file (at 6 minutes 15 seconds): ESD to ISO - YouTube