How to use disk cleanup .

• Temporary Setup Files: Created by a program when it was being installed. These files are no longer needed and can be removed.
• Downloaded Program Files: ActiveX controls and Java applets downloaded automatically from website you’ve visited.
• Temporary Internet Files: Visited web pages that are stored on the hard drive (called caching). These files are re-used the next time you visit a cached web page making the Internet seem faster.
• Offline Webpages: Very similar to Temporary Internet Files but Offline Webpages are entire web pages that are deliberately saved on the hard drive for “offline” browsing.
• Debug Dump Files: Left by Windows after a crash to help fix the problem that caused the crash.
• Old Chkdsk Files: Saved lost file fragments by the chkdsk tool. These files can be removed.
• Previous Windows Installation(s): Files from a previous Windows installation. These files are left after you’ve upgraded the computer to Windows 7. If you don’t need any of the files from your previous Windows installation, you can save a huge amount of space by removing them.
• Game Statistics Files: Stores game statistics for supported games like Solitaire, and Minesweeper.
• Recycle Bin: Files you delete are moved to the Recycle Bin so you can un-delete them later if needed. Emptying the Recycle Bin usually frees up the most space.
• Setup Log Files: Files created when software is being installed. If an installation goes bad these log files are use to troubleshoot what went wrong.
• System Error Memory Dump Files: Created during a system crash for troubleshooting purposes.
• System Error Minidump Files: Created during a system crash for troubleshooting purposes.
• Temporary Files: Programs sometimes save files temporarily for various reasons. These files are usually not important and can be deleted without problems.
• Temporary Windows Installation Files: Created during the installation of Windows and can be removed.
• Thumbnails: Small versions of all of the pictures, video, and supported documents for quick viewing when you are browsing Windows. If you delete these they will be re-generated the next time you are browsing files. You just a-soon leave these files alone.
• Files Discarded by Windows Upgrade: Files identified as system files that were not moved during an upgrade. If your computer is running like it should you can remove these.
• System archived Windows Error Reporting: Files used for error reporting and solution checking with Microsoft. If a program crashes these reports are sent to Microsoft for a solution on fixing the problem. You can delete these files because they’ve been sent to Microsoft.
• Per User Archived Error Reporting: Same as System archived Windows Error Reporting, but on a per-user basis.
• System Queued Windows Error Reporting: Error reports that have not been sent to Microsoft yet or have not been resolved. I do not suggest deleting these files.
• Per User Queued Windows Error Reporting: Same as System Queued Windows Error Preporting, but on a per-user basis.
• Windows Upgrade Log Files: Created when Windows was upgraded. If all of your software and settings are working fine you can delete this too.