Update via wifi (not connected to your computer).
How to install iOS 6
iOS: How to update your iPhone, iPad, or iPod touch
Tip - Be sure and backup your iPad before the iOS update.
Thanks for this. I hadn't seen the wireless update article before but unfortunately, having backed up, when I select the wireless update from the iPad, it tries to verify the update and then tells me it can't as I'm no longer connected to the Internet - which I am as other apps work and the speed test shows 50mb of broadband.