Thanks. When I connect my i-phone or i-pad I can see the device where you indicate and manage it. Unfortunately my apple TV doesn't show up here. This is even though it appears to connect to i-tunes, rent films etc etc. In the previous version of i-tunes it was there on the left hand side under devices.
You can also reveal the sidebarn in iTunes (opt-cmd-S), but it probably isn't there either. (By the way it is there for me)
Your library may have become a secondary (streaming only) library only (it is possible to turn syncing off by ctrl-clicking on the Apple TV listing in the device list and choosing 'Turn Off Syncing" from the contextual menu) and you need to reconnect your library as a primary library.
Navigate to Settings > Computers > Your Library on the Apple TV, you may be told you will lose all synced content, but you can sync it back afterwards, you won't lose any purchased content that has yet to be transferred. Then select Settings > Computers > Connect To iTunes, note the passcode that appears on screen, click on the device in iTunes and enter the passcode when prompted.