Late 2008 Apple Aluminium MacBook complete reinstall

I have a pretty old Aluminum Macbook (late 2008). I pretty much have the original MacOS installation, continuously upgraded to Mac OS Yosemite. Nowadays, it is kind of hard to get by with 250 GB of HD, so I thought about upgrading to a bigger HDD.

I kind of have the feeling that a clean reinstall of MacOS after 6 years of running it would be a good idea, at the same time I do not know where the original installation CD is left. Is there a way to install Yosemite directly??