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Windows 8.1 support ended on January 10, 2023
Update to Windows 8.1 from Windows 8 - Microsoft Support
Go back to Windows 8.1 - Microsoft Support
Install the Windows 8.1 Update (KB 2919355) - Microsoft Support
Which version of Windows operating system am I running?
Create installation media for Windows - Microsoft Support
Upgrade to Windows 10: FAQ - Microsoft Support
Install the latest updates for Windows - Microsoft Support
Updated capabilities to upgrade Windows 8.1 and Windows 7
System requirements - Microsoft Support
How to refresh, reset, or restore your Windows 8.1 PC