Hi, this turned out to be a lot more complicated than I thought, but here is what you do. Find: Joomla root -> components -> com_content -> views -> category -> tmpl -> default_articles.php - Copy that file to your template -> html -> com_content -> category folder. This creates an override so you don't need to make changes to the core files, which you should never do. Open the file you copied to your template directory.
In that file, around line 63, you'll see this:<th class="list-title" id="tableOrdering">
<?php echo JHtml::_('grid.sort', 'JGLOBAL_TITLE', 'a.title', $listDirn, $listOrder) ; ?>
</th>
Change JGLOBAL_TITLE to what ever text you wish to have in place of the title - be sure it has the single quotes around the text.
To change the created date text, find this, line 69:<?php if ($date == "created") : ?>
<?php echo JHtml::_('grid.sort', 'COM_CONTENT_'.$date.'_DATE', 'a.created', $listDirn, $listOrder); ?>
Replace COM_CONTENT_'.$date.'_DATE with your text.
Any other headings you might come across will be in this file also, the second parameter in the JHtml arguments is the text. Be aware that any changes you make here will affect all "List Layouts" on the site. Hope that helps.