Hi,
The images are defined in the CSS of HikaShop. So if you need extra or other images, you can just add your own CSS to define your own images, that you can place wherever you want.
Just look at the image with the developer tools of your browser and you'll see the class and the CSS associated with each one. You'll see that the CSS class uses the "image" parameter in the class.
For example, with the parameter 'user2', you get the class icon-48-user2
And then, if you check the CSS of HikaShop, you can see this code corresponding to it:
span.hkIcon.icon-48-user2 {
background-image: url("../images/icon-48/flatgrey/account.png") !important;
}