Update OnClick Event After Clicked Once?

I am trying to update the .onclick event after its been clicked once. Everything works fine in my script except updating the .onclick event. I have searched the web and found that I should do the following:
div.onclick = function(params);
or
div.onclick = new function(){updatedStatement};

I have tested both of these steps in IE and FF with no luck. Here is my code:
function movePhrase(OPT,MENU,ID,DIR,LEVEL){
if(DIR == "up"){
var num = OPT - 1;
}else{
var num = OPT + 1;
} .....
function newOnClcik(opt,menu,id,level,dir){
var string = "movePhrase("+opt+","+menu+","+id+",'"+dir+"',"+level+")";
return string;
}

Below is an example or the div code I am trying to update:
<div id="downImage1">
<img id="down1" src="images/downArrow.JPG" onmouseover="this.src='images/downArrowPressed.JPG'" onclick="movePhrase(1,20,331,'down',1)" onmouseout="this.src='images/downArrow.JPG'" width="40" height="40" />
</div>