Change home navigation menu text to images

I’ve struggled with this for hours now and simply can’t figure out how to do it..

http://www.feywildecosplay.com/

At the top where the little menu navigation buttons are, it says “the Front” “the Girl Behind The Wig”… ect… I want to replace those all with buttons that I’ve designed.. like so.

http://www.feywildecosplay.com/wp-content/uploads/2014/06/the-front.png

I want to know the most painless and easy way to accomplish this.

Things I’ve tried:

-Inspected the element from google chrome’s editor, saw that the first button was called…

li id = “menu-item-390”

Ive searched high and low through the editor and cannot find the mysterious “menu-item-390” and have no clue where it is located.

I’ve also tried searching desperately for where exactly the text for each button is currently in the code… But I can’t find that info either anywhere.

As you can see, my understanding of code is very poor. But I’m really more concerned with just getting the result quickly.

Thanks!