Q: I just upgraded my entire music library to iTunes Plus. My iPod touch still contains all of the old versions of the newly upgraded tracks. I manage my iPod content manually.
Is there a quick and easy way to replace the old tracks on the touch with the new “Plus” versions?
A: Unfortunately, this is one of the limitations of managing your iPod content manually rather than using automatic synchronization. In manual management mode, your iPod is treated as a completely separate library with no direct association to the tracks in your iTunes library on your computer. As a result, iTunes doesn’t really have any idea which tracks match up between the devices.
Without switching to automatic sync, which would replace everything on your device, your only solution is going to be to manually transfer these tracks to your iPod touch as you would for any other tracks. Provided the iTunes Plus upgrade did in fact replace the original tracks in your iTunes library, and these are the same versions of the tracks you previously copied to your iPod touch, you should be able to re-transfer them and overwrite the existing tracks.
You can also track down all of your iTunes Plus tracks by creating a Smart Playlist.