Adding alt text to NexGEN gallery

looking for some help here. I have been trying to add alt text to my gallery images for some time now, and they’re not showing up when updated in the media gallery. Where should I be updating my theme? `<?php get_header(); ?>
<div class=”inner-container”>
<div class=”band chief”>
<div class=”container”>
<?php if(function_exists(‘simple_breadcrumb’)) { simple_breadcrumb();} ?>
<div class=”ten columns”>
<?php if(have_posts()) while(have_posts()) : the_post(); ?>
<article id=”<?php the_ID(); ?>” <?php post_class(); ?>>
<?php
$category = get_the_category(get_the_ID());

?>
<div class=”inner-content”>
<h1><?php the_title(); ?></h1>
<div class=”clear”></div>
<?php
if($category[0]->cat_ID==10)
{
?>
<div class=”post-date”><?php
echo “Posted by “.get_the_author_meta(‘display_name’,$post->post_author).” on “.date(‘M d, Y’,strtotime($post->post_date));
?> | <?php comments_popup_link(__(‘Leave a Comment’, ‘themeelephant’), __(‘1 Comment’, ‘themeelephant’), __(‘% Comments’, ‘themeelephant’)); ?></div>
<?php
}
else
{
?>
<div class=”post-date”><?php the_time(__(‘M j, Y’, ‘themeelephant’)); ?> <?php //_e(‘author’, ‘themeelephant’);?> <?php //the_author_posts_link(); ?></div>
<?php
}
?>
<?php the_content(); ?>
<?php //edit_post_link(); ?>
<?php //wp_link_pages(); ?>
</div>

</article><!–blog post–>
<div class=”clear”></div>
<?php
if($category[0]->cat_ID==10)
{
?>
<?php comments_template(); ?>
<?php
}
?>
<?php endwhile; ?>
</div><!–end ten–>
<aside class=”sidebar six columns” style=”padding-top:25px;”>
<?php dynamic_sidebar(‘sidebar_standard’); ?>
</aside>
</div><!–end container–>
</div><!–end band–>
</div>
<?php get_footer(); ?>
`
I’m using that code in my single.php. Where should I put the code for alt text, and what should that code be?