Press the Home key, then press the Menu key, and then select "Settings" from the Home menu.
From Settings screen, press the Menu key, and then select "Update Your Kindle".
Alas, that's not possible if you are permanently outside Whispernet range.
Clearly, you can download the update without Whispernet, and of course you can copy it to your Kindle. But, if I've read it right, that's as far as you can go.
If you are permanently outside Whispernet (as I am), you cannot get to the Settings screen. That's because the Kindle has no way of knowing that it's registered to you. To get to Settings, you have to get past the screen that tells you to register. Which means you can't install the update
If I'm wrong about this, someone please correct me.