var isImg = true;
function switch(){
if(isImg){
document.getElementById("img").style.display = "none";
document.getElementById("swf").style.display = "block";
} else {
document.getElementById("img").style.display = "block";
document.getElementById("swf").style.display = "none";
}
isImg = !isImg;
}
<div id="swf" style="display:none;">тут свф</div>
<div id="img">тут img</div>
<input type="button" onclick="switch()">