One way is to go to the black and white adjustment layer and then simply lower the saturation all the way.
One way is to go to the black and white adjustment layer and then simply lower the saturation all the way. Another option is to add a Channel Mixer adjustment layer, and it offers some more control. It allows you to manipulate the red, blue, and green channels individually, and this can be used to adjust the tone and contrast of the final B&W image.