Your iPod uses the iTunes program to download, or sync, all of your computer's applicable media files to your iPod. There are two sync modes in iTunes: automatic and manual. Automatic sync mode automatically syncs your iPod with your computer every time it's connected. This can be a tiresome process because your computer will delete all of your media off your iPod then upload all of your computer's media back onto it. This can also be detrimental if you often clear media files off your computer to save memory. Luckily, putting your iPod into manual sync mode alleviates these problems and allows you to pick and choose which files you'd like to sync or delete from your iPod.
Insert your iPod USB cable into your computer's USB port and connect the other end to your iPod.
Wait for iTunes to load and don't sync your media if you are prompted to do so.
Select your iPod from the "Devices" section in the "Source" pane. This opens a summary of your iPod's settings and will allow you to change sync modes.
Select "Manually manage music and videos" then click "Apply" to save your settings. You can now manually add and delete music from your iPod.