If you use the Start Menu “Search Files and Programs” and type uninstall, it’ll give you a search result Uninstall a program. From there, you can look through your installed apps for once you don’t want to keep. If you bought your computer from a manufacturer (and didn’t built your PC yourself [!]), you might have pre-installed software that you’ve never used or simply don’t need in the future. It’s a very good idea to backup your computer before removing programs.
Over time Windows accumulates files you don’t need to keep anymore. The Disk Cleanup program that comes with Windows allows you to search for and delete many of those files.
If you use the Start Menu “Search Files and Programs” and type cleanup, it’ll give you a Disk Cleanup option. You should be able to Select Drive C: and click Ok. The first scan is a little bit faster, but might not give you all the delete options you’ll want. The scan can potentially take several minutes. You can delete these files relatively safely, but you should also see a button for cleanup system files. If you’ve done a lot of Windows updating, you’ll want to do that scan periodically as well and delete the unneeded files.