Rename “Portfolio” slug?

I have a WordPress theme that I am working with called “Forte”. Yes, it is a premium theme. I have reached out to the developer but apparently he doesn’t really want to help in this situation. Well I need to change the “portfolio” slug to something else. “Portfolio” doesn’t really work at all with the website I am working on. In the past what I’ve done is find ‘rewrite’ => array(“slug” => “portfolio”), in functions.php and I would change it to ‘rewrite’ => array(“slug” => “NEW-SLUG-NAME”),. However, in this theme the developer seems to do it differently. Below is the code in a file called pix_post-types.php which seems to handle this. I am not a PHP developer but I can do a good deal of editing and understand it more-or-less. I would really appreciate some help!

<?php
add_action('init', 'register_testimonial');

function register_testimonial() {
  $args = array(
    'labels' => array(
  'name' => __( 'Testimonials' ), 
  'singular_name' => __( 'Testimonial' ),
  'add_new' => _x('Add new', 'testimonial'),
  'add_new_item' => __('Add a new testimonial'), 
  'edit_item' => __('Edit testimonial'),
  'new_item' => __('New testimonial'),
  'view_item' => __('View testimonial'),
  ),
'capability_type' => 'page',
'has_archive' => false,
'hierarchical' => false,
'menu_position' => 22,
'public' => false,
'singular_label' => __('Testimonial'),
'show_ui' => true,
'supports' => array(
  'title',
  'thumbnail',
  'editor',
  'custom-fields',
  'revisions')
  );

  register_post_type( 'testimonial' , $args );
}

add_action('init', 'register_portfolio');

function register_portfolio() {
  $args = array(
'labels' => array(
  'name' => __( 'Portfolio' ), 
  'singular_name' => __( 'Portfolio' ),
  'add_new' => _x('Add new', 'portfolio'),
  'add_new_item' => __('Add a new item'), 
  'edit_item' => __('Edit item'),
  'new_item' => __('New item'),
  'view_item' => __('View item'),
  ),
'capability_type' => 'page',
'has_archive' => true,
'hierarchical' => false,
'menu_position' => 20,
'public' => true,
'rewrite' => true,
'singular_label' => __('Portfolio'),
'show_ui' => true,
'supports' => array(
  'title',
  'thumbnail',
  'editor',
  'excerpt',
  'trackbacks',
  'custom-fields',
  'comments',
  'revisions')
  );

      register_post_type( 'portfolio' , $args );
    }

add_action( 'init', 'create_portfolio_taxonomies', 0 );

//create two taxonomies, genres and writers for the post type "book"
function create_portfolio_taxonomies() 
{
  // Add new taxonomy, make it hierarchical (like categories)
  $labels = array(
'name' => _x( 'Galleries', 'taxonomy general name' ),
'singular_name' => _x( 'Gallery', 'taxonomy singular name' ),
'search_items' =>  __( 'Search Gallery' ),
'all_items' => __( 'All Galleries' ),
'parent_item' => __( 'Parent Gallery' ),
'parent_item_colon' => __( 'Parent Gallery:' ),
'edit_item' => __( 'Edit Gallery' ), 
'update_item' => __( 'Update Gallery' ),
'add_new_item' => __( 'Add New Gallery' ),
'new_item_name' => __( 'New Gallery Name' ),
'menu_name' => __( 'Galleries' ),
  );    

  register_taxonomy('gallery',array('portfolio'), array(
'hierarchical' => true,
'labels' => $labels,
'show_ui' => true,
'query_var' => true,
'rewrite' => array('hierarchical' => true )
  ));

  // Add new taxonomy, NOT hierarchical (like tags)
  $labels = array(
'name' => _x( 'Tags', 'taxonomy general name' ),
'singular_name' => _x( 'Tag', 'taxonomy singular name' ),
'search_items' =>  __( 'Search tags' ),
'popular_items' => __( 'Popular tags' ),
'all_items' => __( 'All tags' ),
'parent_item' => null,
'parent_item_colon' => null,
'edit_item' => __( 'Edit tag' ), 
'update_item' => __( 'Update tag' ),
'add_new_item' => __( 'Add New tag' ),
'new_item_name' => __( 'New tag name' ),
'separate_items_with_commas' => __( 'Separate tags with commas. They will be used for filtering portfolio items' ),
'add_or_remove_items' => __( 'Add or remove tags' ),
'choose_from_most_used' => __( 'Choose from the most used tags' ),
'menu_name' => __( 'Tags' ),
 ); 

  register_taxonomy('portfolio_tag','portfolio',array(
'hierarchical' => false,
'labels' => $labels,
'show_ui' => true,
'query_var' => true,
'rewrite' => array( 'slug' => 'portfolio_tag' ),
  ));

}

            /*=========================================================================================    */

?>