While studying the effect of variation of intensity on the photocurrent, intensity of light is changed in a photocell by

Intensity (I) of radiation at a distance ‘r’ from monochromatic source of power ‘P’ is $I = \frac{P}{4{\mathrm{\pi r}}^2}$. 

From the above relation, the intensity decreases with increase in the distance of light source.

Hence, intensity of light is changed in a photocell by changing the distance of light source from the emitter.