Objective:

To delete all the rows that have been added to the Form Grid when a field value is changed

Code:
<script>
$(document).ready(function(){
    var selectField = "field1";
    var formGrid = "field2";

    //when select box value is changed
    $("[name="+selectField+"]:enabled").change(function(){
        //remove all data from form grid
        $("[name="+formGrid+"]").find("table tr.grid-row").remove();
    });
});
</script>