I went for the clean install for each update. It was then quite easy to make the ISOs. But, for those who updated their Wind 8.1 etc, and have the .wim, maybe, if you can be bothered, this will help. It is just one of many sites offering the same.
http://www.ehow.com/how_5750929_convert-wim-file-iso-file.html
Frankly, I would suggest, unless you are a real testing enthusiast, you are wasting your time. MS appear to have taken the unusual step of offering selected builds, as they work through it. You could end up with quite a large number of useless burned ISOs!! I have a couple of laptops with Windows X installed from the ISO. Only noticeable difference is it gets rid of the double login picture.
I have no idea what went on between MS and private sites, but I read that many of the pages offering the ESD converter, have been closed. Rather odd really. The method has been around for some years. There iare alternatives, but theu require a little more work. IMGBurn is one:
Link Removed
Reference the Wim/Esd thing. I can follow the argument that you get one or the other, according to how you use the upgrade, (no idea of why that choice occurs), but, for users who have not been down that road, the .Wim is the file used for "Windows to go", which, as is known, is only available in the Enterprise edition.