Change “posts” label to “articles”.

Paste in functions.php


add_filter(  'gettext',  'change_post_to_article'  );
add_filter(  'ngettext',  'change_post_to_article'  );

function change_post_to_article( $translated ) {
     $translated = str_ireplace(  'Post',  'Article',  $translated );  // ireplace is PHP5 only
     return $translated;
}