Here is a sample that you can work into your current code to do this.
function showControl()
{
var control = document.getElementById("control")
var currentText = control.innerHTML;
if (currentText == "Play")
{
control.innerHTML = "Pause";
}
else
{
control.innerHTML = "Play";
}
}
</script>
<a href="#" id="control" onclick="showControl();">Play</a>
Drew