how do I upgrade security to WPA3on Mac 14

Your Router must support that protocol, and the change must be made in your Router.

You connect to your Router using the administration portal (typically based on its IP address) enter your Router administration credentials, and change the Router settings.

Once enabled inside your Router, just change the Mac settings in:

system preferences > network > Wi-Fi ...

...to match.

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If you have an ethernet connection to your Router, this will be simple. If not, it will disconnect when you make the change in the Router, and not reconnect until you make the corresponding change in your Mac.