The syncing process is the hard connection between your iOS device and your computer, helping you to transfer, back up, and download content. To make it easier there are options to automatically bring over content like music and podcasts without having to sort through it, but this does allow you slightly less control for what you are bringing over. If you have limited space on either your iPhone or computer then you may not want to have everything go back and forth, and if one device is specifically for business then a full audio library may not be appropriate. In these cases there is the option to manually control the content that is on your iPod, iPad, or iPhone, and this can help you even further customize your device.
The basic premise of the manual device management is that you will bring over just the content that you want from each sub-section, like iBooks or Videos, instead of the entire Library. Many iPhones or iPads pale in comparison to the storage space of your computer, so if you have two weeks of solid music on your iTunes you may not be able to put that all on your iPod Touch to go jogging with.
To start, begin a regular syncing process by plugging your iPhone into your computer. Go into iTunes and then select the device from under the Devices heading in the left hand panel. In the main Summary tab you can select the option that says, “Manually manage music and videos.” This will be in the Options section, towards the bottom, above the Configure Universal Access button. At the very bottom right hand corner, under the Revert button, will be the Apply button. You will choose this as you do after you make any substantial changes to the sync.
Now that you have done this you will have a completely different syncing process for getting content over. Instead of having the content selected in the tabs that appear when you select the iPhone from under the Devices heading, you will drag and drop the items from the Library onto the iPhone in the left hand panel. The name of the item will have a green circle with a white plus sign appear on it, which indicates that it is being added. Once you have added everything that you want to be on the iPhone you can choose to sync it again in File.
This process will not actually get rid of the audio or other content that is already on there through the old syncing process, but it will ensure that other media will not automatically go on there without being selected.