A Code to update table using wordpress. 

  $wpdb->update( 'wordpress_background', array( 'background' => $background, 'url' => $url ), array( 'id' => $id ), array( '%s', '%s' ), array( '%s' ) );

here the is description

$wpdb->update( 'table', array( 'column1' => 'value1', 'column2' => 'value2' ), array( 'ID' => 1 ), array( '%s', '%d' ), array( '%d' ) );