How do I delete multiple tracks in Traktor?
Select you tracks (individual by holding ctrl on keyboard and clicking individual tracks or selecting 'a bunch' of tracks (multiple tracks) by click on the first track, hold shift and click the last track), right click on a selected song, choose 'delete from playlist' or 'delete from collection' (witch you prefer).
How do I delete a folder in Traktor?
If you want to get rid of a whole folder in Traktor you have to delete all the tracks in that folder. Then the folder will be gone.