If I understand you correctly, you have a system which came preinstalled with Windows 8, but without a physical product key (sticker), and you would like to install Windows 8.1 onto this system. In some cases, manufacturers have made use of firmware embedded
product keys as are described in this Microsoft Support article:
KB 2796988. If your system is one such system, installation of the proper media will automatically detect the applicable key. This will require that if the system originally came installed with Windows 8, you use Windows 8 media to install, then use the
Windows Store to update to Windows 8.1.
If your system does not contain a firmware embedded product key, or if you are unsure, it would be recommended to contact the system manufacturer. If you do not have the installation media intended for the system, you may also need to request installation
media from the manufacturer.
Brandon
Windows Outreach Team- IT Pro
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