How to change your computer's IP? (using proxies)

I want to change a computer's IP (the kind of IP ipchicken.com or whatismyipadress.com shows you). I don't know how to go about this. :/ Anyway, how would I do this? I've tried this:

      WebProxy myProxy = new WebProxy("http开发者_如何学JAVA://69.136.69.228:27977/", true);
                 myProxy.Credentials = CredentialCache.DefaultNetworkCredentials;
                 req.Proxy = myProxy;

Thanks for all your help in advance.

The external IP is set by your provider - you can't change it on your computer.