To get started, click the "Website" tab in the left-hand editing pane:

Then, click the "Content" tab in the left panel.

Then, in the menu that appears, select "Files & media":

Next, mouse over the item you'd like to download and click "Edit" on the right hand side:

Hover over the image in the new window that appears:

Finally, right click on the image and select "Save Image As..." to save the image to your computer!