The wait is over! After a long wait, Apple have released iOS 6 into the wild. You can get it right now in two ways. On your iOS device, tap on settings, go to general and click on software update to get the update delivered straight to your device over your wi-fi network. Alternatively, you can plug your iOS device into your computer, connect it to iTunes and update from there.
Although the update is available right now, I strongly advise that you wait a couple of days for the initial rush to die down. As usual, a lot of people will be rushing to get the update installed on their iOS device so the download speeds will be sl0w.