Why can't I get rid of files?

[JackCatalano]

I try to get rid of files but I can't.   I will click "This PC>Windows C> Windows. It will say something to the effect of "You need the administrator" or "You don't have Permission". Also, it will say something to the effect of "You need Permission. You require permission from TrustedInstaller to make changes to this folder."

How do I go about eliminating some of my files when I get messages like I just mentioned?

[Salmon Trout]

You're not supposed to delete files from the Windows folder. They are usually system files needed to keep Windows running. The files you need to delete (or shift to somewhere else) are files you have put on the disc yourself. These could be games, movies, etc?