How to adapt pic-size in "recommend pics" on frontage?

I’am new with customizr and I am actually evaluating whether i will work with this theme or with another. I have worked several hours with customizr. It’s a flexible and interesting theme, although it has it’s tricks.

So I could not find out how to edit the start page , especially not the 3 round pics! where is the default Start Page of customize to edit?