Software update apple-tv doesn't work - servers not available

Had the same problem, but got an answer under another topic here and it worked out just fine. Choose "General" > "Network" > "TCP/IP" > "Configure manually". Skip the IP, Subnet Mask etc by just clicking "done" and change the DNS to 008.008.008.008 Then try to start the update process once again and it should start downloading it immediately. Worked for me in US as well as in Estonia.

Apple doesn't recommend using DNS settings other than those provided by your ISP. If you are going to use this method, make sure you put them back when finished.

and that's what I did, just after the update was finished and everything works great.