Probably full of cr@p, needs a clear out, you can also move stuff from C to another drive.
But I am guessing you are loaded with stuff that needs removing.
Use CCleaner and IObit Advanced systemcare for starters, both free downloads.
Open downloads in C drive to see all the stuff you don't need, which will be most of it. Just right click on each one then click delete, it will free up space. When that is done, run Ccleaner again to empty the bin...
There is other stuff, but try that first...