Front page content boxes: change to pictures instead of FA icons

Hi guys,

I’m new to all of this, so please bare with me.

I would like to have pictures instead of the FA icons in my Front Page Content Boxes. I read a lot about how to change them, but I cannot get it to work. I know a lot of people have asked the same question before, but I don’t know what else to do. Could someone please post an easy to follow guide on how I can change them to have pictures?

thank you so much,
Cindy