title: Can't change default thumbnail size
body: <p>I'm making gallery in wordpress and I want to change default thumbnail size but it doesn't work properly. When I set photo as post thumbnail natural size is 150x150 in wordpress media options I changed thumbnail size to 215 143.</p>
  
  <p>in functions I have </p>
  
  <pre><code>add_theme_support( 'post-thumbnails' );
  
  if ( function_exists( 'add_theme_support' ) ) {
      add_theme_support( 'post-thumbnails' );
          set_post_thumbnail_size( 1240, 1240 );
  }
  </code></pre>
  
  <p>My gallery query:</p>
  
  <pre><code>&lt;ul id="stage"&gt;
                  &lt;?php
                  // The Query
                  $the_query = new WP_Query( array( 'post_type' =&gt; 'flota', 'orderby' =&gt; 'title', 'order' =&gt; 'ASC' ) );
  
                  // The Loop
                  while ( $the_query-&gt;have_posts() ) : $the_query-&gt;the_post();
  
                  $thumbnail = wp_get_attachment_image_src( get_post_thumbnail_id ( $the_query-&gt;ID ), 'thumbnail' );
                  $full = wp_get_attachment_image_src( get_post_thumbnail_id ( $the_query-&gt;ID ), 'full' );
  
                  $cats = wp_get_object_terms( $post-&gt;ID, 'flota_category' );
  
                  $items = array();
                      foreach ( $cats as $cat ){
                          $slug = $cat-&gt;slug;
                          $items[] = $slug;
                      }
                      $counter = count($cats);
                      $i = 0;
  
                  ?&gt;
  
                  &lt;li data-tags="&lt;?php 
                      foreach ( $items as $tag ){
                          if (++$i === $counter ){
                              $tags = $tag;
                          }
                          else{
                              $tags = $tag . ', ';
                          }
                          echo $tags;
                      }
                  ?&gt;"&gt;&lt;a href="&lt;?php echo $full[0] ?&gt;" rel="lightbox[flota]"&gt;&lt;img src="&lt;?php echo $thumbnail[0] ?&gt;" width="215" height="143" style="background:#ffffff;"&gt;&lt;/a&gt;&lt;/li&gt;
  
                  &lt;?php
                  endwhile;               
                  ?&gt;      
  &lt;/ul&gt;
  </code></pre>