Verified answer

Best way is to save important documents and files either to a disk or flash drive. Then start deleting junk files and programs that you don't use anymore that are taking up room on your hard drive. The do a disk cleanup, defrag and run and up to date anti virus and spyware cleaner on your system.

Method 1 : Backup your photos and songs and other stuff you feel is needed to an external source ( CD/DVD/ External HDD/Thumbdrive), reinstall OS and all programs.

Method 2: Delete all temp folders and files related to your User account and internet cache, run AV utilities and Spyware removal, perform and defrag on the HDD and remove unwated programs with the " ADD/REMOVE programs feature" in Control panel.

There is a good program they let you try it free for 30 days without paying and in 1 day, today, you'll have your computer tuned up so download it below and run it. It's called tune up utilities

If you mean unused programs. Just uninstall the programs you don't use. Or save the stuff you want to an external drive, and wipe your computer.