I need resize poster: width: 212 — Height: 320

Okay thanks. Now open functions.php file (inside theme folder), find this line:

add_image_size('img200300', 200, 300, true);

After that line add this code:

add_image_size('img212320', 212, 320, true);

Now open single.php file and find this line:

<img class="bw_poster" alt="<?php the_title_attribute(); ?>" src="<?php $image_id = get_post_thumbnail_id(); $image_url = wp_get_attachment_image_src($image_id,'img200300', true); echo $image_url[0]; ?>">

and change img200300 become img212320.

Good luck