The more you use your computer, the more temporary files are created on it. Temporary files being with a purpose, but are supposed to be, as the name describes, temporary - removing themselves when their purpose is finished. Many times, they don't remember to remove themselves when they are finished with their purpose. Removing these files allows your computer to run more efficiently, and makes it easier to detect and remove undesired files like files from a virus infection for example. Here is how to use the Windows 7 Disk Cleanup Utility:

1. Click on Start, then All Programs, then Accessories, then System Tools, then Disk Cleanup.
2. Select the drive you want to clean, and click OK.
3. Disk Cleanup will now analyze the drive for files that can be removed.
4. Click on Clean up system files to include temporary files related to the Windows operating system.
5. Select which files are to be removed from your computer by checking the appropriate boxes, then click OK, then Delete Files.
6. Finally, you can click on the More Options tab to remove unused programs and extra System Restore points.
7. Click on Clean up in the Programs and Features section, then OK to open the Programs and Features window.
8. You can remove any unnecessary programs by clicking on the name of the program, then uninstall.
9. To delete all but the most recent System Restore point, click on the Clean up button in the System Restore and Shadow Copies section, then click on Delete.
10. To finish using Disk Cleanup, click OK, then Delete Files. The unnecessary files will now be removed from your computer.