You will need to edit the single-portfolio.php file in the theme directory. If you are using the child theme that comes with the theme, you can create a new file with the same name in the child theme directory and then copy over the code from the parent to edit it. This way your changes will last during updates to the parent theme.
You will need to change line 76 to remove ninecol class –
<div class="entry-content">
and delete lines –