find the coded for the iamge, for example:
image: new google.maps.MarkerImage('plugins/webassist/google_javascript/images/pushpin_pacifica.png', new google.maps.Size(40,41), new google.maps.Point(0,0), new google.maps.Point(7,38)),
shadow: new google.maps.MarkerImage('plugins/webassist/google_javascript/images/pushpin_shadow.png', new google.maps.Size(40,41), new google.maps.Point(0,0), new google.maps.Point(7,38)),
and change the path to point to your custom images.