You can change the settting via E-COMMERCE > DISPLAY OPTIONS > PAGINATION NAVIGATION
(And immediately above that new setting, is where you can increase your window/paging size).
Smaller numbers give faster loading times for google, and lower bandwidth consumption (for most customers who don't look at the photos).
Bigger numbers are better for customers who want to browse the photos.
Product List with default pagination
default pagination replaced with Show More button. Clicking Show More will append the page with the next set of images.