You definitely do not want to touch winsxs, these are the side by side assemblies for loading DLLs, COM objects, interfaces ect. You can download Disk Usage (DU) and run it against your whole disk
Disk Usage Run it as du -l 1 C:\ Then repeat and target large directories to narrow down what's using up space. You may also have a hidden hibernate file which will be the same size as your RAM I tend to turn off hibernate to free up space. From a command prompt
powercfg /h:0ff