<!DOCTYPE html>
<html>
<head>
<script  runat="server">
Sub ChangeFont(obj As Object, e As EventArgs)
      button1.Font.Name = "Courier New"
      button1.Font.Size = FontUnit.Parse("10")
End Sub
</script>

</head>
<body>

<form runat="server">
<asp:Button id="Button1" Text="Change" Font-Name="Verdana" Font-Size="15" runat="server" OnClick="ChangeFont" />
</form>

</body>
</html>