iTunes Match and Mac Operating System

I have installed iTunes Match on my Mac, which has an operating system of 10.5.8. When I go to my iPhone 5 to turn iTunes Match on, it says that I have not subscribed to this service. In doing some research, it seems my operating system is too old to support iTunes Match and allow it to sync with my iPhone. What do I need to do to update my operating system to get the iTunes Match working properly? Will my photos and music remain on my computer if my operating system is updated?