the popular pod shows the information for the product that is ordered most.
What are you trying to do?
a) Change the product that is shown in the popular pod?
if so, set the gateway to none and place an order for a whole bunch of whatever product you want to be the most popular
b) Change the image for the product shown in the popular pod?
if so, edit the product that is being shown in the popular pod, and change it's image.