How can I change the number of results per page with the WordPress plug-in?

This can be accomplished by adding a swiftype_search_params_filter in your theme’s functions.php.

function swiftype_search_params_filter($params) {
     $params['per_page'] = 10;
     // update the value to your desired # of pages

     return $params;
}

add_filter('swiftype_search_params', 'swiftype_search_params_filter', 8, 1);