It depends on what you want to clean:
Without Administrator: You can clean your browser caches, user temporary files, application caches, and all privacy traces. These are the most common cleaning tasks and work without any elevated privileges.
With Administrator: Cleaning system-level items requires running as Administrator. This includes system temporary files (C:\Windows\Temp), Windows Update cache, installer cache, prefetch files, font cache, delivery optimization cache, old Windows installations, and system-level crash dumps.
If you run RJL System Cleaner without Administrator privileges, the system-level cleaners will be grayed out in the sidebar with a note: "Run as Administrator to clean system files." Everything else works normally.
To run as Administrator: Right-click RJLSystemCleaner.exe and select "Run as administrator."