Solved:
wp-includes –> post-template.php –>
function prepend_attachment($content) {
$p = '<p class="attachment">';
$p .= get_the_attachment_link(false, true, array(400, 300));
$p .= '</p>';
$p = apply_filters('prepend_attachment', $p);
return "$p\n$content";
}
Change the array(x,y) to whatever maximum value you want!
