At about mid-day today, Apple made the iOS 6 software update for current model iPhones, iPads, and iPod touches available for download.
To install the software, you can connect your supported iPhone, iPad, or iPod touch to a Wi-Fi network and download the software update over the air.
The over the air update can be started by tapping:
Settings > General > Software Update
For the more traditional crowd, you can connect your supported iDevice to your Mac or Windows PC running iTunes 10.7 and download and install the software update using your sync cable.