How to remove a bed slat holder (without breaking it)
These slats curve upwards just a little bit. Pull upward in the center of the slat, pushing one of the ends into its socket at the same time. The slat has enough flexibility to curve just a little more and clear the other socket. 

Start in the center of the bed, this is where the frame has more flex and it is easier to work out how to do it.

HTH