iframe {
   display:none;
}

var iframearray = document.getElementsByTagName("iframe");
iframearray[0].style.display = "block";
var visibleFrame = 0;

<input type="button" onClick="hideNext" />

function hideNext(){
iframearray[visibleFrame ].style.display = "none";
visibleFrame++;
iframearray[visibleFrame ].style.display = "block";
}