New versions of Knox are tied to a specific Android Operating System. Each time you upgrade your OS, Knox is also upgraded – you can't "download" or "install" a newer version of Knox on it's own.
For example, if you recently upgraded your device to Android P, your Knox version is also automatically upgraded to Knox 3.2.1.
To check if your device is capable of a Knox upgrade.
- Check the Android version that you need for your device to run Knox. Before installing this Android version, do some research on the changes that come with the new version.
- Check the Android version currently on your device: Settings > General > About device > Android version.
- Check the software updates that are currently available: Settings > General > About device > Software update > Update.
- Install the Android update. (Availability depends on your carrier and country. If you are unable to upgrade your Android OS, then you can't upgrade to a newer version of Knox.)