This is how you can change labels for default content types of WordPress. In this example we change ‘Posts’ to ‘News’.

Here’s the PHP  code to put in your functions.php

//Change posts labels
function xiong_change_post_label() {
    global $menu;
    global $submenu;
    $menu[5][0] = 'News';
    $submenu['edit.php'][5][0] = 'News articles';
    $submenu['edit.php'][10][0] = 'Add news article';
    $submenu['edit.php'][16][0] = 'Tags';
}
function xiong_change_post_object() {
    global $wp_post_types;
    $labels = &$wp_post_types['post']->labels;
    $labels->name = 'News';
    $labels->singular_name = 'News article';
    $labels->add_new = 'Add new';
    $labels->add_new_item = 'Add new News article';
    $labels->edit_item = 'Edit News article';
    $labels->new_item = 'News article';
    $labels->view_item = 'Show News article';
    $labels->search_items = 'Search for News article';
    $labels->not_found = 'Could not found News articles';
    $labels->not_found_in_trash = 'Not even in trash can';
    $labels->all_items = 'All News articles';
    $labels->menu_name = 'News';
    $labels->name_admin_bar = 'News';
}
 
add_action( 'admin_menu', 'xiong_change_post_label' );
add_action( 'init', 'xiong_change_post_object' );