If you don’t see an item named Software Update (on my unmanaged Ventura M1) in System Settings or System Preferences, click the Spotlight icon in the corner of your screen, then type Software Update in the search field. From the search results, choose Software Update.
If your older Mac doesn’t include Software Update, use the App Store app instead. It’s in your Applications folder. Click the Updates tab in the App Store to check for updates, or search for software by name.