the www and not www problem

Hello, I run a blog named http://uit.ro but when I install it I didnt chosen www in fron of the url.

I have 2 questions:
– how do I add www. in front of the url without reinstalling wordpress
– if I keep the blog without the www is actualy http://www.uit.ro redirect to uit.ro? I ask this becouse I know if you run a site with and without wwww in the same time is considered duplicate content.