How i can edit a xml file using DOMDocument and xquery

First of all, your document has invalid XML syntax (the </createCDATASection> tag). FTFY:

<events date="06-11-2010">
  <event id="8">
    <title>Proin porttitor sollicitudin augue</title>
    <description><![CDATA[Lorem  nunc.]]></description>
  </event>
</events>
<events date="16-11-2010">
  <event id="4">
    <title>uis aliquam dapibus</title>
    <description><![CDATA[consequat vel, pulvinar.]]></description>
  </event>
  <event id="1">
    <title>You can use HTML and CSS</title>
    <description><![CDATA[Lorem ipsum dolor sit amet]]></description>
 </event>
</events>

Now, here's a solution to edit title/description for your event:

$dom = new DOMDocument;
$dom->loadXML(file_get_contents('doc.xml'));

$xpath = new DOMXPath($dom);
$nodes = $xpath->query('//event[@id="4"]/title | //event[@id="4"]/description');

// title
$node = $nodes->item(0);
$node->nodeValue = 'hello world';

// description
$node = $nodes->item(1);
$cdata = $node->firstChild;
$cdata->replaceData(0, strlen($cdata->data), 'hello world description');

print $dom->saveXML();