It depends what type of license you have:
Download Windows 7 Disc Images (ISO Files) - Microsoft
Microsoft doesn't supply them for OEM preinstalled licenses (Dell, HP, etc.).
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If preinstalled:
Or you can use this for preinstalled OEM or Retail Licenses. This is on a first come, first served monthly basis.
Download the correct ISO file and make your own disk and use the Product Key that is on the COA Sticker.
https://www.heidoc.net/joomla/technology-science/microsoft/67-microsoft-windows-and-office-iso-download-tool
Download: Windows ISO Downloader.exe