Windows 7 USB/DVD Download Tool creates a bootable flash drive from a downloaded.iso file, or disk image, of Windows 7. Users need a 4GB USB drive to install Windows 7 on a PC without an optical drive. Most netbooks run Windows XP, so only a “clean” upgrade to Windows 7 is possible. The tool is a 947KB file that can be downloaded from Microsoft’s site (download.exe file) Users need to back up data and application settings before upgrading, restore and reinstall applications.”]
Source: https://www.csoonline.com/article/2124499/microsoft-unwraps-netbook-windows-7-upgrade-tool.html