Cropping an existing image in a project is pretty straight forward.
Simply select the desired image within the template and click the crop icon in the top toolbar.
Once you click the crop button you'll then be able to click and drag the frame border to expand the amount of the image you want to display.
It's important to note that we keep a crop frame that's proportional to the frame within your template. That means that you won't normally be able display 100% of the contents of the image, because the frame in the template won't allow it.