Rename order status Completed to Processed

Add below code to your active themes functions.php or custom plugin file 

function rename_wc_order_status( $statuses ) {
    foreach ( $statuses as $key => $status ) {
        $new_status[ $key ] = $status;
        if ( 'wc-completed' === $key ) {
            $statuses['wc-completed'] = _x( 'Processed', 'Order status', 'woocommerce' );
        }
    }
    return $statuses;
}
add_filter( 'wc_order_statuses', 'rename_wc_order_status' );