Ordinarily, the car will download an update in the background, without telling you, and then tell you that it's available and ask if you want to apply it. If yours is asking you to connect to WiFi, then that sounds like something else is happening. Perhaps there's a problem with your Internet connection -- even if you're connected to WiFi, if that connection is blocked from connecting to the Internet (or even just to Tesla's servers), it could be the problem. You might want to review your WiFi router's settings, and if you can find nothing wrong either contact Tesla or take the car to somewhere with public WiFi. (Tesla's stores have WiFi to which the car will connect automatically, or so I've heard.) You might need to leave it parked for a while before the car will grab the update, though.