Deploy web application amazon

I have a web site hosted in amazon, the website project is in svn and the amazon server is a m1.medium.

The problem is that I made a lot of modification (new features and a transfer from svn to git), and i don 't know how to deploy the new version of the website without shutting down the server.

The solution I am going to try is to launch a new instance in amazon, configure it and then change the server ip (to make www.mysite.com redirect to the new site). But someone told me is better to copy the instance I'm using now and just make my change in this new instance.

I don't know what is the best, especially about the machine (m1.medium is old right ?) so I need your advices.

Also What is the advantage of RDS, now the database server and the website server are in the same instance.