<!DOCTYPE html>
<html>
<head>
<style>
table, th, td {
border: 1px solid black;
}
</style>
</head>
<body>
<p>Click the button to change the value of the rowspan attribute, from 2 to 1, of th with id "myTh".</p>
<table>
<tr>
<th id="myTh" rowspan="2">Month</th>
<th>Savings</th>
</tr>
<tr>
<td>January</td>
<td>$100</td>
</tr>
<tr>
<td>February</td>
<td>$100</td>
</tr>
</table>
<br>
<button onclick="myFunction()">Try it</button>
<script>
function myFunction() {
document.getElementById("myTh").rowSpan = "1";
}
</script>
</body>
</html>