With the changes to Itunes 11, I struggled finding a couple of features. First, the left side-bar was missing.

Hide or show the left side-bar by clicking CTRL-s (or CMD-s).

The other thing I struggled with was finding the option to Manually manage music and video. It was quite easy once I found it. The problem was that it was hidden below the fold.

• Go to your device (iPod, iPhone, or iPad), and click on the Summary section.
• From the Summary section, scroll down.
• The option is located just above the Reset Warnings button.
• Then it's simply checking or unchecking the box and clicking Apply.