You need to do the following in a child theme, do not make changes to the theme itself.
EDIT
I had a good look at the ‘Heuman’ theme. I think to solve your problem here is to copy the following files to your child theme, content.php and archive.php
Rename your content.php to something like content-archive.php. Open it up and delete the following lines
<?php if (ot_get_option('excerpt-length') != '0'): ?>
<div class="entry excerpt">
<?php the_excerpt(); ?>
</div><!--/.entry-->
<?php endif; ?>
and replace it with
<div class="entry content">
<?php the_content(); ?>
</div><!--/.entry-->
Next, open up your archive.php and replace he following line
<?php get_template_part('content'); ?>
with
<?php get_template_part('content', 'archive'); ?>
That should solve your problem