563464 wordpress category appearance change

Hello, I need one straight forward change in our wordpress blog - when you click on specific category the site display all posts inside this category. In every category we have subcategories and we want following : When you click on main category to see static text on top which I will provide for all categories and below instead list of the posts, a list of all subcategories which are in the main category. I will give you a sample how it should look - nothing complex. Just this - a list of subcategories instead list of the posts. Thank you