To reduce size of WinSxS folder on a running version of Windows OS you can run couple commands.
Command line utility (cmd or powershell) must be ran as Administrator!
To determine the actual size of the WinSxS folder, use this command:
dism.exe /online /Cleanup-Image /AnalyzeComponentStore
Now we can reduce its size by running this command:
dism.exe /online /Cleanup-Image /StartComponentCleanup
To remove all superseded versions of components in component store, use this command:
dism.exe /online /Cleanup-Image /StartComponentCleanup /ResetBase
To reduce amount of space used by Service Pack, use this command:
dism.exe /online /Cleanup-Image /SPSuperseded
The service pack cannot be uninstalled after this command is completed.
Also you can “compact” running os by running this command:
compact.exe /CompactOS:always