title: How to override a parent theme's add_image_size and $content_width in the child theme's functions.php
body: <p>I am trying to override some functions in a parent theme, 
  I want to override <code>add_image_size</code> from 590 to 800 and <code>$content-width</code> from 590 into 850.</p>
  
  <p>Here is the functions.php of the parent theme.</p>
  
  <hr>
  
  <pre><code>class WPEX_Theme_Class {
  
      public function __construct() {     
          // Theme setup: Adds theme-support, image sizes, menus, etc.
          add_action( 'after_setup_theme', array( &amp;$this, 'setup' ), 10 );
      }       
  
  
      public function setup() {
          // Set content width variable
          global $content_width;
          if ( ! isset( $content_width ) ) {
              $content_width = 590;
          }
  
          // Add theme support        
          add_theme_support( 'post-thumbnails' );
  
          // Add image sizes
          add_image_size( 'wpex-entry', 590, 9999, false );
          add_image_size( 'wpex-post', 590, 9999, false );
      }
  
    $blogger_theme_setup = new WPEX_Theme_Class;
  } 
  </code></pre>
  
  <hr>
  
  <p>This is my try:</p>
  
  <pre><code>function __construct() 
  {
       add_action('after_setup_theme', array($this, 'change_theme'));
  }
  
  function change_theme() 
  {
      remove_action('add_image_size', 'setup');
      add_action('wpex-post', array($this, 'setup'));
  }
  
  function setup() {
  
      add_theme_support( 'post-thumbnails' );
  
      // Add image sizes
      add_image_size( 'wpex-entry', 800, 9999, false );
      add_image_size( 'wpex-post', 800, 9999, false );
  
   }
  </code></pre>
  
  <p>It is not working, what do I need to change?  </p>