The following example shows you how you can change the header height on a TitleWindow container in Flex by setting the headerHeight style.
Full code after the jump.
<?xml version="1.0" encoding="utf-8"?>
<!-- -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
layout="vertical"
verticalAlign="middle"
backgroundColor="white">
<mx:ApplicationControlBar dock="true">
<mx:Form styleName="plain">
<mx:FormItem label="headerHeight:">
<mx:HSlider id="slider"
minimum="24"
maximum="64"
value="32"
snapInterval="2"
tickInterval="4"
liveDragging="true" />
</mx:FormItem>
</mx:Form>
</mx:ApplicationControlBar>
<mx:TitleWindow id="titleWindow"
title="The quick brown fox jumped"
status="{titleWindow.width}x{titleWindow.height}"
titleIcon="@Embed('assets/TitleWindow.png')"
showCloseButton="true"
headerHeight="{slider.value}"
borderColor="haloBlue"
borderAlpha="1.0"
width="400"
height="150">
<mx:VBox id="vBox" width="100%" height="100%">
<mx:Label text="{vBox.width}x{vBox.height}" />
</mx:VBox>
</mx:TitleWindow>
</mx:Application>



very good!