Download CCleaner (it's free) tick all the boxes, and run the program. All it will do is get rid off all the rubbish you do not need.
Windows is a compressed program. When you fire it up Windows needs to expand the start up files into empty disk space, use it, then compress it Again. It does that many, many times as part of the boot up
If you have less than about ten percent of your hard drive free then you will lose everything very soon. Windows will will not load if it cannot have access to about ten percent
