At the WinHEC conference in China, Microsoft has announced several new details about the release of Windows 10, including that all pirated copies of Windows can be upgraded for free. If you are wanting to upgrade to Windows 10, take a look at the matrix below, as it outlines your options for installing the OS.
To no surprise, Microsoft will offer upgrades of Windows 10 via ISO and Windows Update. Generally speaking, if you are running the latest version of Windows 7 or Windows 8, you will have the option to use an ISO or streamline the update process by using Windows Update. For all other iterations of Windows 8 and 7, your only options will be to use an ISO.