Where did you download this theme from?
Its not downloaded, its a custom theme.
Where did you obtain the theme from?
its using the basic twenty thirteen functions.php but the rest is custom.
I dont know how else to answer this questions. I build websites. It is a custom HTML & CSS theme, using a bootstrap grid that. I designed it in photoshop. It is using a basic twentythirteen functions.php.
http://codex.wordpress.org/Template_Hierarchy
if the theme is based on Twenty Thirteen, then a single post will use single.php, which in turn will call content.php which contains the code for the featured image. https://codex.wordpress.org/Post_Thumbnails
to avoid the featured image being shown on single posts, you will need to wrap that code into a if( !is_single() ) conditional statement.
however, as your theme is a custom development, this is just a guess, as you are the only one with full access to the files.
I think that could be the answer? Whats the best way to wrap an if statement in another if statement?
<?php if ( has_post_thumbnail() && ! post_password_required() ) : ?>
<div class="entry-thumbnail">
<a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>" >
<?php the_post_thumbnail('full', array('class' => 'img-responsive')); ?>
</a>
</div>
<?php endif; ?>
try
<?php if ( has_post_thumbnail() && ! post_password_required() && !is_single() ) : ?>
spot on! Thank you for your help π