How do I uninstall OS X?

I think my Mac is just too old and small for the Yosemite program

MacBook Pro (13-inch, Mid 2009)
Processor 2.26 GHz Intel Core 2 Duo
Memory 4 GB 1067 MHz DDR3

So...now that I have installed it - is there a way to uninstall it?

Thank you for all your help

via ehMac.ca http://ift.tt/1P0PaC0