You can update directly from your Apple TV by going to Settings alas this is for third generation Apple TV’sonly. 2nd gen is updated to 6.2.1 with no new icons, no Beats, etc.
This is the first time that the 2nd generation units have been left behind the 3rd generation. The 3rd Gen needs a refresh badly so there’s no incentive for 2G owners to upgrade right now.
I’m largely disappointed apple hasn’t moved Apple TV further. I wish watches were a hobby, and Apple TV meant something more than adding flat icons and Beats applications.