I was trying to switch off displaying of creation and last modification date in item view, but without success. I have even tried to modify the /components/com_k2/templates/default/item.php in "date created" section - also no success.

I also need to switch off author box.

Can anybody explain me how to do it?

I know, that it's a little bit odd, but customer knows better...

All you have to do is to Disable them through the category's settings under Item View.
There is no need to mess up with the core files of K2 for these issues.

Thanks! You solved my problem. I was looking for global option and there's no such thing.