Please Help on Pages and Headers!

First I want to add a header but the theme limits me 300 by 125? That is too little. Secondly my pages are labeled as categories in my menus. I did it this way because I have sub pages and I want it to every time I post it goes to that sub page and main page. For example if you go to my site is topcitysneakers.com when you click Nike page it has 3 articles and you see the drop down menu you click Nike Basketball you see and article and that also has another dropdown Lebron James. These are categories and I want them to be pages but I don't know how to link them together? Please help. Thank you.