I recently noticed that the free space on the 60GB OS partiton on my laptop was running very low on space. Some of this was due to old offline files which I managed to cleanup fine.
I then ran Tree Size on the OS partition and found that the winsxs folder was 10.2GB.
After a bit of research I managed to use the command below and reduced the winsxs by 4GB :)
DISM /online /Cleanup-Image /SpSuperseded
The command needs to be run from an elevated command prompt and you cannot uninstall the Service Pack after it completes
I then did the same on my desktop and recoverd an almost identical ammount.