<html>
<head>
<script>
function displayResult()
{
document.getElementById("myHeader1").rowSpan="2";
}
</script>
</head>
<body>
<table border="1">
<tr>
<th id="myHeader1">Month</th>
<th id="myHeader2">Savings</th>
</tr>
<tr>
<td>January</td>
<td>$100.00</td>
</tr>
<tr>
<td>February</td>
<td>$10.00</td>
</tr>
<tr>
<td>March</td>
<td>$80.00</td>
</tr>
</table>
<br>
<button type="button" onclick="displayResult()">Change rowSpan for the first cell</button>
</body>
</html>