How to destroy Codeigniter library instance

I would like to know if there is any way I can destroy a Codeigniter library instance.

What I want to do is something like this:

$this->load->library('my_library');
/**
    Code goes here
**/
$this->my_library->destoy_instance();
The reason I need to do this is because I need to liberate RAM memory while executing a large scripts.

Any help will be greatly appresiated.