Hello. I have on my site Disqus comment available and also I've turned on option for related articles. But unfortunatetly to me, comment place is below related articles. I'd like to change it and have possibility of comments straight below ending an any article. Where I can change it? And how to do this permanently (don't want to this again and again after every upade of joomla or k2).

Greetings

You can do this by overriding K2's templates.
More on overriding can be found here: getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates

Furthermore the item.php file is well commented and all you need to do is located the comments block from its HTML comments and paste it to your desired location.