i found
Editing file "/templates/ja_findus/error.php" in template "ja_findus".
Line 80 to 90
this lines are for the text
<div class="wrap-text">
<div class="error-msg"><h2><span><?php echo $this->error->getMessage(); ?></span></h2></div>
<div id="error-message">
<p><?php echo JText::_('JERROR_LAYOUT_PLEASE_TRY_ONE_OF_THE_FOLLOWING_PAGES'); ?></p>
</div>
*i think this one is for the button*
<div class=btn-home>
<a href="<?php echo $this->baseurl; ?>/index.php" title="<?php echo JText::('JERROR_LAYOUT_GO_TO_THE_HOME_PAGE'); ?>"><?php echo JText::('JERROR_LAYOUT_HOME_PAGE'); ?><span class="icon"></span></a>
</div>
but i want to customise the error 404
1-i want to put a .gif instead of the big "404"
2- i want to insert text with an email to warn me, if member found a 404 error
i think there is a better way like to put an article to 404, but i am new with joomlart 🙁