I installed K2 and it looks really good but I'm a little bit afraid what will happen after Joomla update? K2 can be not compatible with new Joomla version and I'll lose all migrated to K2 articles?

Hi. Can you please be more specific ? Currently K2 works with all the major Joomla! releases ( 1.5.26, 2.5.19, 3.2.3 ) so i don't see the reason for worrying. There is also a recent blog post regarding the future of K2 at getk2.org/blog/1792-k2-v268-released-whats-coming-in-v270-a-v3-update.