Mac storage basics · Apps and macOS itself
Where do macOS updates download to, and can I delete them?
Short answer: In a protected system area you shouldn't touch. Install the pending update or let macOS clean it up; free more space and retry if it fails.
Software Update keeps downloaded updates in a protected system area that you can't (and shouldn't) delete by hand. If an update is downloaded but not installed, either install it or wait — macOS cleans up stale update files on its own over time, and a restart often clears a failed preparation.
If an update is stuck or failing for lack of space, free more room and try again from System Settings → General → Software Update.