itunes playlist sync issues

After having created several itunes playlists in my mac, within garmin express, I have transferred them to the 645, however, I cannot see the same plalists in garmin express as those that appear in the garmin device (in fact, there are fewer playlists in the device than in garmin express)

On then hand, I have deleted from within garmin express some playlists but the songs in that playlists are still in the device, it seems as if the sync process for garmin express with the device is not working properly.

Is there anyway to force syncing garmin express playlists with the device?

What is the best way to delete all the playlist and music from the device and start from scratch?

Thanks for your help.