I’ve figured it out –

1. add your new icon to this folder: wp-content/themes/eunoia/images/icons/iconbox/

2. when referencing the new icon – just add your new icon filname eg: [iconbox_top title=”View Our Portfolio” icon=”Heart.png”]

…I had to make a few css changes because we wanted no colour background, border radius, and we changed the icon pixelsize..but if you are just doing the same sized icon you should be fine.