При нажатие на динамическое изображение оно должно меняться на другое

<script>
Image0=new Image();
Image0.src="https://www.cyberforum.ru/images/bird_10_points.png" 
Amount=3;
 
 
Ypos=new Array();
Xpos=new Array();
Speed=new Array();
rate=new Array();
grow=new Array();
Step=new Array();
Cstep=new Array();
nsSize=new Array();
ns=(document.layers)?1:0;
WinHeight=(document.layers)?window.innerHeight:window.document.body.clientHeight;
WinWidth=(document.layers)?window.innerWidth:window.document.body.clientWidth;
for (i=0; i < Amount; i++){                                                                
 Ypos[i] = Math.round(Math.random()*WinHeight);
 Xpos[i] = Math.round(Math.random()*WinWidth);
 Speed[i]= Math.random()*10+10;
 Cstep[i]=0;
 Step[i]=Math.random()*0.1+0.05;
 grow[i]=10;
 nsSize[i]=Math.random()*1+5;
 rate[i]=Math.random()*0.5+0.1;
}
if (ns){
for (i = 0; i < Amount; i++){
document.write("<LAYER NAME='sn"+i+"' LEFT=0 TOP=0><img src="+Image0.src+" name='N' width="+nsSize[i]+" height="+nsSize[i]+"></LAYER>");
d
 
 
}
 
}
else{
document.write('<div style="position:absolute;top:10px;left:10px"><div style="position:relative">');
for (i = 0; i < Amount; i++){
 
document.write('<img id="si" src="'+Image0.src+'" style="position:absolute;top:10px;left:10px;filter:alpha(opacity=100)">');
 
}
document.write('</div></div>');
}
function bubbles(){
var WinHeight=(document.layers)?window.innerHeight:window.document.body.clientHeight;
var WinWidth=(document.layers)?window.innerWidth:window.document.body.clientWidth;
var hscrll=(document.layers)?window.pageYOffset:document.body.scrollTop;
var wscrll=(document.layers)?window.pageXOffset:document.body.scrollLeft;
for (i=0; i < Amount; i++){
sy = Speed[i]*Math.sin(190*Math.PI/180);
sx = Speed[i]*Math.cos(Cstep[i]);
Ypos[i]+=sy;
Xpos[i]+=sx; 
if (Ypos[i] < -50){
Ypos[i]=WinHeight+50;
Xpos[i]=Math.round(Math.random()*WinWidth);
Speed[i]=Math.random()*54+6;
 
grow[i]=5;
nsSize[i]=Math.random()*1+5;
}
if (ns){
document.layers['sn'+i].left=Xpos[i]+wscrll;
document.layers['sn'+i].top=Ypos[i]+hscrll;
 
}
else{
si[i].style.pixelLeft=Xpos[i]+wscrll;
si[i].style.pixelTop=Ypos[i]+hscrll;
si[i].style.width=grow[i];
si[i].style.height=grow[i]; 
 
}
grow[i]+=rate[i]; 
Cstep[i]+=Step[i];
if (grow[i] > 10) grow[i]=11;
}
setTimeout('bubbles()',10);
}
bubbles();
 
 
 
 
  
  
</script>