$entity = \Drupal::entityTypeManager()->getStorage('node')->load($nid);
$entity->set('title','Titulo de nuevo nodo');
$entity->set('field_custom_field', $value);
$entity->save();
$entity = \Drupal::entityTypeManager()->getStorage('node')->load(1);
$entity->delete();
\Drupal::entityTypeManager()->getStorage($entity_type)
->delete([$id1 => $entity1, $id2 => $entity2]);