Apple Announced Yosemite 10.10 and iWorks Suite Update for Yosemite at special Event on 16 OCT , As Free Update . You can download and update your existing mavericks installation with Yosemite , from app store.
Compatible Devices ( Website) :
-iMac (Mid 2007 or newer)
-MacBook (Late 2008 Aluminium, or Early 2009 or newer)
-MacBook Pro (Mid/Late 2007 or newer)
-MacBook Air (Late 2008 or newer)
-Mac mini (Early 2009 or newer)
-Mac Pro (Early 2008 or newer)
-Xserve (Early 2009)
You can download Yosemite from app store : https://itunes.apple.com/in/app/os-x-yosemite/id915041082?mt=12
RAM : 2GB
HDD : 8GB
OSX 10.6.8 or later currently running .
Appstore to Download the update