functions.phpに下記コードを追加

function change_post_menu_label() {
  global $menu;
  global $submenu;
  $menu[5][0] = 'INFORMATION';
  $submenu['edit.php'][5][0] = 'INFORMATION一覧';
  $submenu['edit.php'][10][0] = '新規追加';
  $submenu['edit.php'][16][0] = 'タグ';
}
function change_post_object_label() {
  global $wp_post_types;
  $labels = &$wp_post_types['post']->labels;
  $labels->name = 'INFORMATION';
  $labels->singular_name = 'INFORMATION';
  $labels->add_new = _x('新規追加', 'INFORMATION');
  $labels->add_new_item = '新規追加';
  $labels->edit_item = '編集';
  $labels->new_item = '新規記事';
  $labels->view_item = '記事を表示';
  $labels->search_items = '記事を検索';
  $labels->not_found = '記事が見つかりませんでした';
  $labels->not_found_in_trash = 'ゴミ箱に記事は見つかりませんでした';
}
add_action( 'init', 'change_post_object_label' );
add_action( 'admin_menu', 'change_post_menu_label' );