How to free the disk space of my pc in order to optimize storage and speed?

I am using windows 10 OS in my system. I don’t use any other antivirus or third-party firewall. I even don’t have that much data in my pc. I have some doc files and visual studio but still my local drive is completely filled. I don’t think that it is happening due to any malware because I have active windows 10 defender. Kindly, suggest me that even with this small amount why is my local disk is completely filled (complete and red) and how to optimize my memory storage?