Click on the picture to select it. This will activate the Picture Tools link above the ribbon. Click the Picture Tools link to reveal all the options relating to pictures.
The Crop tool is located on the right side of the Picture Tools. Click the crop tool and you will notice that there are "crop" handles around the border of the picture. Drag these handles to remove the excess elements that are unnecessary to the picture.
Note - It is important to note that even though the picture has been modified by cropping, these extra elements are simply hidden from view and are still part of the picture. Think in terms of a piece of paper that you rolled partly up. The items on the rolled part are still there, but simply hidden from view.