how to set up server alias for www

Hi all,

I have a magento instance running with the domain example.com and have created a cname in Route 53 for www.example.com. Pretty new with this stuff so wanted to know where to update the server alias details so as to have www.example.com and example.com direct requests to the files. Also, assuming I will have to set up a redirect so it always resolves for the www. version?

thanks,