WinSxS folder stores Windows Packages, about it some are not needed anymore.

To clean it you need to do as follows:

Search for “cmd”  (without the quotes)    in the start menu, no rx right click on cmd.exe and click run as administrator then run the following in the command prompt:

dism /Cleanup-Wim

This does as follows:

Deletes resources associated with a mounted image that has been corrupted.
This command will not unmount a mounted image, ampoule nor will it delete images that
can be recovered using the /Remount-WIM command.

Also Run:

dism /Online /Cleanup-Image /spsuperseded

This does as follows:

WARNING! The service pack can’t be uninstalled after this operation is
completed. This operation will remove backup files created during service
pack installation. Use /hidesp switch to hide the service pack from Installed
Updates.

The explaination for the switches can be found here:  technet.microsoft.com/library/dd744382(WS.10)

dism –

DISM enumerates, installs, uninstalls, configures, and updates features
and packages in Windows images. The commands that are available depend
on the image being serviced and whether the image is offline or running.

As always I am not responsible for any damages that may happened.  Do this at your own risk.

Please put a nice comment if this helped you!