All depends on what OS you have installed, how old your Mac is and what version of the applications you have.
If the Mac was bought after mid October 2013, and you have Mavericks installed, all the iWork applications are free to download from the Mac App Store.
Mavericks installed to download and install the latest version of Keynote which is 6.2.
If you don't have Mavericks post back with details of; OS version, model of Mac and where you purchased iWork from.
Dear Gary, Thanks fr the prompt reply
My Mac Book is relatively old - Probably - 2010 MacBookPro 6.2 , Processor- Intel Core i5 OSX - 10.9.4 (13E28) Pages - 5.2 Numbers - 2.3.
I probably didn't get iWork. Only Pages and Numbers . Because i use Office for Mac i have not been missing iWork. Now i wish to switch. What do i do
One option, which I would recommend, is to buy the iWork DVD containing Keynote version 5.3, from Ebay, they are ready available and very low priced. Keynote 5.3 in many ways is more advanced and stable than version 6, and many users prefer version 5. Also version 6 does not successfully open version 5 files.
The other option is to upgrade to Mavericks and upgrade all your existing applications, I would not recommend this for the reasons above in your situation.