I'm guessing here since I do not own a DP-50F, but check for set screws along the edge of the tonearm base. It may be recessed into the back or there could be two of these set screws. You would need to loosen both set screws and manually grab the tonearm pivot and pull the arm up to set the desired height.
The tonearm may be like the one on my original stock DP-62L. The tonearm's height adjustment was controlled by two set screws that manually locked the vertical tonearm height adjustment.
The arm was mounted in a collar that was a long tube that slid down into the arm mounting collet. The two set screws, recessed in the collet, locked onto this tube and locked the tonearm into the proper height.