For the image of the category there is an option inside the general K2 parameters called "Placeholder image for category if none exists" where you can place "Hide" and you can get rid of this default photo of the category if you haven't put any.
Now to remove the subcategory all you have to do is set the option inside the categorys' parameters called "Catalog mode" to "No" and adjust on the "Category view options" what information of the category you would like to display.
