Hi suba,
i)You can delete your temporary files stored in temp folder.
Start--->Run--->%temp%
Select all the file and press ctrl+delete to delete all temporary files.
ii) You can use CCleaner software to delete all the temporary internet files and folder. It is freeware only.
iii) Uninstall the unwanted softwares, because it takes unnecessary space in your C: drive.
I hope it will helps you.