Change the slugs of project post, project category and project tags, add this to your child theme functions.php, once you've changed the slug on line 5, 20 & 38, go to your dashboard and go setting/permalinks and just hit the save button to update the slugs

functions.php

/*Change Project Post Type Slug*/
function ds_divi_modify_project_post_slug() {
    return array(
    'feeds' => true,
    'slug' => 'new-slug', /*Change text between brackets*/
    'with_front' => false,
    );
    }
add_filter( 'et_project_posttype_rewrite_args', 'ds_divi_modify_project_post_slug' );

/*Change Project Category slug*/
function ds_divi_modify_project_catagory_taxonomy() {
    // get the arguments of the already-registered taxonomy
    $project_category_slug_args = get_taxonomy( 'project_category' ); // returns an object

    // make changes to the args
    // in this example there are three changes
    // again, note that it's an object
    $project_category_slug_args->show_admin_column = true;
    $project_category_slug_args->rewrite['slug'] = 'new-category-slug'; /*Change text between brackets*/
    $project_category_slug_args_args->rewrite['with_front'] = false;

    // re-register the taxonomy
    register_taxonomy( 'project_category', 'project', (array) $project_category_slug_args );
}
// hook it up to 11 so that it overrides the original register_taxonomy function
add_action( 'init', 'ds_divi_modify_project_catagory_taxonomy', 11 );

/*Same as above but changes the slug of the Project Tag*/
function ds_divi_modify_project_tag_taxonomy() {
    // get the arguments of the already-registered taxonomy
    $project_tag_slug_args = get_taxonomy( 'project_tag' ); // returns an object

    // make changes to the args
    // in this example there are three changes
    // again, note that it's an object
    $project_tag_slug_args->show_admin_column = true;
    $project_tag_slug_args->rewrite['slug'] = 'new-tag-slug'; /*Change text between brackets*/
    $project_tag_slug_args_args->rewrite['with_front'] = false;

    // re-register the taxonomy
    register_taxonomy( 'project_tag', 'project', (array) $project_tag_slug_args );
}
// hook it up to 11 so that it overrides the original register_taxonomy function
add_action( 'init', 'ds_divi_modify_project_tag_taxonomy', 11 );