<html>
<head>
<script type="text/javascript">
function changeText()
{
var x=document.getElementById("mySelect")
x.options[x.selectedIndex].text="Melon"
}
</script>
</head>
<body>
<form>
Select your favorite fruit:
<select id="mySelect">
<option>Apple</option>
<option>Orange</option>
<option>Pineapple</option>
<option>Banana</option>
</select>
<br /><br />
<input type="button" onclick="changeText()" value="Set text of selected option">
</form>