Hi,
Check K2 category settings, each of them have long list of available options.
But if you don't find there you have to delete link manually here:
templates\gk_ThemeName\html\com_k2\templates\default\item.php
find & remove html href:- Code: Select all
<a class="itemImage modal" rel="{handler: 'image'}" href="<?php ........ </a>