I installed K2 in my old joomla 1.5 (I know I have to upgrade it X) havent had the time nor the need) but I cant find any way or option to reply to particular comments in the blog

I can only post new comments, and there's no way to make individual replies (or not that I can find it) is there any plugin or any way to enable/add this?

Hi. K2 comments are flat. There is no reply functionality. If you need to this you can search for plugin that can integrate Facebook or DISQUS comments in K2.