We decided to do an "Upgrade", as this is easier way to go for Windows 10 and more users use it. The user is not asked for the Windows activation code. We tried to create an ISO and you can even make an ISO with 32-bit and 64-bit ISO file, and this needed a 6GB USB or a doual layer DVD. In case you go for ISO instalataion, Microsot needs the activation code for the WIndows 10. Microsoft wants you to do a clean install of new WIndows 10 with the ISO inslataion.  Before upgrading to Windows 10 we made a system image backup. You can do it by launching Windows? own built-in system image tools. The alternative is to use third party software.
System GoBack Free  is another great tool if you want to go back to your old Windows. Just do not forget to create a backup of your system before upgrading.With the System GoBack tool you can create system backup using one click. After a backup is created you can safely run Windows upgrade using MediaCreationTool. If you decide to do back to the old Windows, System GoBack will do the job. Microsoft is also providing a tool for a Windows 10 Rollback. The shortcoming of the Windows 10 rollback tool is that it only allows users to rollback to previous OS within a month.