<?php

$dom = new DOMDocument();
$dom->formatOutput = true;
$dom->loadXML('<data>
<post>
    <deal_id>479</deal_id>
    <deal_title><![CDATA[Δίπλωμα Μηχανής, στη Σχολή Οδηγών Παραστατίδης στον Εύοσμο, μόνο με 49€]]></deal_title>
    <deal_url>http://d...content-available-to-author-only...n.com/site/shop/autokinito-el/diplwma-mixanis-sxoli-odigwn-parastatidis-euosmos/</deal_url>
    <deal_city><![CDATA[Θεσσαλονίκη]]></deal_city>
    <deal_price><![CDATA[49]]></deal_price>
    <deal_previous_price><![CDATA[125]]></deal_previous_price>
    <deal_discount><![CDATA[60.8]]></deal_discount>
    <deal_start><![CDATA[2016-01-10 00:00:00]]></deal_start>
    <deal_end><![CDATA[2016-04-01 00:00:00]]></deal_end>
    <deal_image>
        <image>
            <file>http://d...content-available-to-author-only...n.com/site/wp-content/uploads/2015/09/c700x420.jpg</file>
            <title>c700x420</title>
            <caption></caption>
            <description></description>
            <alt></alt>
        </image>
        <image>
            <file>http://d...content-available-to-author-only...n.com/site/wp-content/uploads/2015/09/diploma1.jpg</file>
            <title>diploma1</title>
            <caption></caption>
            <description></description>
            <alt></alt>
        </image>
    </deal_image>
    <deal_sales><![CDATA[0]]></deal_sales>
    <deal_active><![CDATA[true]]></deal_active></post></data>');
$root = $dom->documentElement;
/*$doc->getElementsByTagName("deal_image")->("image")->("file")->nodeValue = "Somenthing";*/

//$root   = $dom->documentElement("post");

$featuredde1 = $dom->getElementsByTagName('image');

foreach ($featuredde1 as $node) {
    $node->parentNode->removeChild($node);
}
foreach ($featuredde1 as $node) {
    $node->parentNode->removeChild($node);
}
$data = $dom->getElementsByTagName( "deal_image" );
$data ->item(0)->nodeValue = "http://d...content-available-to-author-only...n.com/site/wp-content/uploads/2015/09/c700x420.jpg";

echo $dom->saveXML();