Remove the cover of the wall switch motion sensor. Some models have a screw located on the face that must first be removed. On other models, the cover just slides off.
Locate the small rotary control marked "S."
Turn the switch counterclockwise to decrease the motion sensor's sensitivity.
Turn the switch clockwise to increase its sensitivity.
Test the sensor's sensitivity by walking across the room or space in your normal manner. Replace the cover when you're satisfied with the setting.