generative modeling for Rhino
they're on by default. If you're not getting them, your machine isn't accessing the McNeel download server. This is either because the server is offline (extremely unlikely, it's maintained by Amazon.com), you are offline, you're behind a firewall that blocks the address, you're behind a virus-scanner/firewall that blocks applications going online or, finally, there's a bug in the update notification code.
There is an item in the Grasshopper Help menu called "Download SDK Help...". This command accesses the same Amazon server. So if that works, we've eliminated at least a few possible culprits.