If you have available space in other two drive, you don't have to delete anything, just move the files you want. Keep your C drive free. Even if you want to install software, make sure you install them on drive D so that your C drive is free and have lots of space. Computer need space to work fast. You might increase RAM if you want more speed. Computer search for scratch memory once RAM is low on C drive. Hence increasing RAM will resolve the issue and you don't have to move anything from the C drive. Also defragmenting the hard disk will speed up the computer. Good Luck :)
I am not in the favor of buying a new RAM for that purpose. My laptop is already more than 3 years old and I just got a new one 2 months back. So, I am really not in the mood to spend again. But thanks for your inputs.