I have 156GB hard drive with only 200MB left of free space. I put all data on an 1000GB external hard drive that I am able to but I still keep bumping up against the limits on the C drive despite virus checking, doing disk cleanup and dumping programs I don't absolutely need. I ran TreeSize Free and it shows that 137GB is Windows and 132GB is Windows Installer. Can I get rid of any of that? What do I look for?