Hi shousro,
You can make change easily by using Google chrome inspect element or Firebug for Firefox. What I usually do is set Compress CSS in Template manager to No, then hover on any HTML element ( div, buttton, image, text, …) you want and right click on it and then click on inspect element, it will show you which CSS class it is using and which CSS file and the path to this element on the right side. then you can go to the file and replace it with new CSS you change.
With the menu, did you mean that you want to display Top menu in the current Main menu? If so, please go to Extensions > Template manager > Your default template > Your profile and change menu type in Menu settings section: http://easycaptures.com/fs/uploaded/711/0629764767.png
Regards.