In USA-regional-maps-inc.php, change <img src="<?php echo $rightURL; ?>" alt="<?php echo $rightTitle; ?>" title="<?php echo $rightTitle; ?>"
width="320" height="240" style="margin: 0px; padding: 0px; border: none"
to adjust the width= and height= values to make the displayed image larger.
Since the NWS Radar has a different aspect ratio than the WU Satellite map, you won't be able to make them the same height, but you can make the image larger (remember to preserve aspect ratio so it doesn't get distorted).
Try using width="480" and removing the height="240" .. that seems to work.