1. Edit file qa-theme/<your-theme>/qa-theme.php
2. Add/Merge the initialize() function so that it looks this way:
public function initialize() {
parent::initialize();
if (qa_get_logged_in_level() < 100) {
unset($this->content['navigation']['main']['user']);
if (qa_request() === 'users')
qa_redirect('');
}
}