New property type to show in header menu

This might all sound either typical or stupid or both. Recently I contracted a website designer to make up a real estate website for me. I have limited funds so didn’t ask for too much and didn’t get much.
Now I’m trying to correct and finish the job myself as the site is about a quarter done.
He has set up pages with sub categories in the menu on the front page all with links to the particular categories so everything appears in the right place. Now I need to add to the categories and have them appear on the header with their correct links only I don’t know how to do it. Can anyone help or give me directions as to where to find information? I promise I’ll come back and ask more questions, please…
My site name is http://www.myheartandmyhome.com.au