New
#11
You need a DVD, not a CD because Windows 10 won't fit on a CD. Not sure if you just lump all the shiny discs together under a common name, but wouldn't want a CD to fail if you meant to be specific by saying CD. To do the upgrade from the ISO file it doesn't really matter if you make a DVD from it, or just mount it. If you are upgrading from Windows 7 then you will need software to do either. If you mount the ISO file you get a fake (virtual) DVD drive letter that appears. If you burn the DVD from the ISO file, then you run the upgrade from the DVD. Just make sure you burn the DVD on a slow speed (I would not go higher than 2X if you have a choice) and set the verify after burning option on the software. It will take longer, but you will know you have a good DVD.
To do an upgrade, you run the setup.exe from within Windows 7/8/8.1 from inside the mounted ISO file or on the DVD. You do not boot from the DVD. That's why it doesn't matter if you burn the DVD first or not. To do the clean install, unless you do something really tricky, you need to boot from a Windows 10 installation DVD or USB flash drive created from the ISO file - so you have to have one made in order to do a clean install. If you make a working USB flash drive or a DVD from the ISO file, you don't need to keep the ISO file if you don't want to - the DVD will do both the upgrade and a clean install. It just depends on if you insert the DVD and run setup.exe while Windows 7/8/8.1 is running (upgrade) or whether you boot the computer from it (clean install).