Click on the icon, select the desired part of the graphic, and doubleclick to eliminate the unwanted parts. I used an image mask for this graphic. I've posted a review of what I did. There are two types of masks. Path masks crop out the edges, and screen out whatever is below them.
Image masks act differently.
A solid black image mask acts transparent. A solid white image mask covers everything below it. Other colors turn into grades of transparency, partially masking out anything below the mask.