Have problems with C partition space

Do you know how to fix partition low space problem? My laptop C partition has a low disk space problem and has already stopped me installing many interesting games. So, I decide to resolve this problem. But, I don’t know what to do. Is it possible for me to fix this problem without buying a new drive? Or I have to replace it with a larger drive instead? Thank you for any suggestion. One more thing, I am using Windows 7.