I understand that you are having issues in accessing your theme's functions.php and not with the code. Write a new plugin (code below) and upload to 'wp-content/plugins' directory and activate it. That's it!
<?php /* Plugin Name: Implement wpautop Version: 1.0.0 Description: Implement wpautop function. */ remove_filter( 'the_content', 'wpautop' ); remove_filter( 'the_excerpt', 'wpautop' );