hook_update_N() example moving blocks

gistfile1.php

<?php
/**
 * Move system user-menu block from header to region-top.
 */
function elmcip_setup_update_7004() {
  $num_updated = db_update('block')
    ->fields(array(
      'region' => 'header_top',
      'status' => 1,
      'weight' => 1,
    ))
    ->condition('delta', 'user-menu')
    ->condition('theme', 'elmcip')
    ->execute();

  print "Moved and enabled $num_updated block(s) to region header-top \n";
}