Can I reformat my MacBook from Os X 10.4 to Os X 10.6?

My Macbook is currently running Os X 10.4 but I want to reformat it because it is running sluggish and I would just like to start anew with it. But I wanted to know if it is possible for me to buy the Os X 10.6 cd to reformat it even though it is running Os X 10.4?