Changing the template style
On the Settings > Visual Link Preview page you can enabled the "Use Custom Styling" setting allowing you to change the style of the visual link.
Here is just one example of what can be achieved by simple playing around with the settings:
Changing the image size
The image size fields expects either the name of a thumbnail size or a specific size in this format: widthxheight
Example thumbnail sizes: thumbnail, medium, largeExample specific sizes: 100x100, 50x50
If you need the thumbnail cropped a specific way we recommend using the Simple Image Sizes plugin to create that thumbnail size.