How to change onclick destination url in parent frame.

Okay i have Main Frame which has an iframe inside it.

in main frame there is image

<td rowspan="3" valign="top"><a href="#"><img src="template_05.gif" width="172" height="45" border="0" onclick="openw('https://www,google.com',0,0,0,0,0,1,1,900,900,200,1,1);" value="openw"/></a></td>

now www.google.com i need to change to www.yahoo.com

i have the code which does it but only in iframe .It doesn't change the main frame img.How can i override it?

<script language="JavaScript">
// THIS IS THE CODE TO CHANGE URL FOR THE CURRENT FRAME
function rpl (){
        var imgs = document.getElementsByTagName("img");
        for(var i = 0; i < imgs.length; i++) {
                var img = imgs[i];
                if(img.getAttribute("value") == "openw") {
                        img.setAttribute("onclick", imgs[i].getAttribute("onclick").replace("https://www.google.com", "http://www.yahoo.com"));
                }
        }
        }
        window.onload=rpl;
</script>

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