Resizing post/article preview image

Hello

I hope this is the correct section to raise such a question.

I was hoping anyone could help me out resizing the preview image that shows in a post/article?

I am using the Cherry – Responsive News and Magazine Theme from themeforest ( http://themeforest.net/item/cherry-responsive-news-and-magazine-theme-/3671130 ). When asking the author he said:
loop.php and pasted in this code:

<?php $timthumb = bdayh_get_option('timthumb');
                    if ($timthumb == true) { ?>
                    <img src="<?php echo BD_URI ?>/timthumb.php?src=<?php echo bd_post_image('large'); ?>&h=158&w=158&zc=1" alt="<?php the_title(); ?>" title="<?php the_title(); ?>" />
                <?php } else { ?>
                <?php
                      $thumb = bd_post_image('large');
                      $ntImage = aq_resize( $thumb, 158, 158, true );
                              if($ntImage == ''){
                                    $ntImage = BD_IMG .'/default_thumb.png';
                                }
                ?>
                    <?php if (strpos(bd_post_image(), 'youtube')) { ?>
                        <img class="youtube-img" src="<?php echo bd_post_image('large'); ?>" width="158" height="158" alt="<?php the_title(); ?>" title="<?php the_title(); ?>" />
                    <?php } elseif (strpos(bd_post_image(), 'vimeo')) { ?>
                        <img class="vimeo-img" src="<?php echo bd_post_image('large'); ?>" width="158" height="158" alt="<?php the_title(); ?>" title="<?php the_title(); ?>" />
                    <?php } elseif (strpos(bd_post_image(), 'dailymotion')) {?>
                        <img class="dailymotion-img" src="<?php echo bd_post_image('large'); ?>" width="158" height="158" alt="<?php the_title(); ?>" title="<?php the_title(); ?>" />
                    <?php } else { ?>
                        <img class="ntImage-img" src="<?php echo $ntImage; ?>" width="158" height="158" alt="<?php the_title(); ?>" title="<?php the_title(); ?>" />
                    <?php } ?>
                <?php } ?>

As I am as green as they come with regards to these things I was not sure what to do with it. So I tried it out in the custom CSS section and adjusted the width and height in different sections but that didn’t work. So I tried the same thing in the editor and the loop.php section but with same results.

Anyone got a got idea on how I might take care of this issue?

Thanks