Some times drive of hard disk contains some temporary files, you can delete those files without any difficulty and they will not affect on your operating system. Suppose windows show you message that disk space on drive C is very low.
You can uninstall any programs such as yahoo messenger, antivirus and other programs which are installed on drive C and you install them on any other drive, where free space is available. For deleting temporary files just right click on your drive C and select properties. Click on the disk cleanup button. a new window will open, here you will see some files which are already checked. You can select all these files for deleting. After selecting those files press the Ok button. By using the same process you can also delete temporary files.