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.