Creating custom styles in FCKeditor

I have purchased a CMS called Flyspeck which uses FCKeditor. I want to remove the default styles in the drop down menu and add my own but can't work out how to do this. One of my customer's websites only requires two styles (main heading & secondary heading) to be listed in the styles drop down menu. I am planning on using Flyspeck/FCKeditor on multiple websites, so would appreciate clear step-by-step instructions on how to modify the default styles, so I can do this myself on future websites.