XML access

Hi everyone !
I’m new in Flash, so i would like some help here…
I’m trying to build a User Interface (SWF) and provide it to my customers in order to have (an easy) access t their sites and they can change the data (images & Texts) of an XML driven photo Gallery.
After i load the XML in Flash(CS4), i can ‘trace’ the nodes at the output panel but when i’m editing new data the changes are not “saved” in the XML…
The Files look like this:

[COLOR=#ffffff]gallery.xml[/COLOR][COLOR=#ffffff]fla[/COLOR]<?xml version=“1.0” encoding=“utf-8”?>
<objects>
<picture_path>pictures/1.jpg</picture_path>
<thumb_path>thumbs/1.jpg</thumb_path>
<picture_desc> abcdefgabcdefg </picture_desc>
<picture_title> ABC </picture_title>

<picture_path>pictures/2.jpg</picture_path>
<thumb_path>thumbs/2.jpg</thumb_path>
<picture_desc> abcdefgabcdefg </picture_desc>
<picture_title> </picture_title>

<picture_path>pictures/3.jpg</picture_path>
<thumb_path>thumbs/3.jpg</thumb_path>
<picture_desc> abcdefgabcdefg </picture_desc>
<picture_title> ABCDEFG </picture_title>
.
.
.
.
</objects>
var captionsXMLLoader:URLLoader = new URLLoader();
captionsXMLLoader.load(new URLRequest(“gallery.xml”));
captionsXMLLoader.addEventListener(Event.COMPLETE, captionsXMLLoadedHandler);

function captionsXMLLoadedHandler(eventObj:Event):void {
var captionsXML = new XML(eventObj.currentTarget.data);

   trace(captionsXML.picture_title[2]);                // [COLOR=#808080]-&gt; ABCDEFG 

[/COLOR]
// [COLOR=#808080]( This line should change the data of XML ? )[/COLOR]
captionsXML.picture_title[2] = “Bla Bla Bla Bla…”;
trace(captionsXML.picture_title[2]); // [COLOR=#808080]->[COLOR=#808080] Bla Bla Bla Bla…[/COLOR][/COLOR] [COLOR=#808080][/COLOR]
[COLOR=#808080][/COLOR]
[COLOR=#808080][/COLOR]
[COLOR=#808080][/COLOR]
[COLOR=#808080][/COLOR]
[COLOR=#808080][/COLOR]
[COLOR=#808080][/COLOR]
[COLOR=#808080]}[/COLOR]

My problem is that i can’t change the data in the XML through AC3 . Is this possible ?
Please some help here !!!