JonDo is the ip changer tool you have to install on your computer. It acts as a proxy and will forward the traffic of your internet applications encrypted to the mix cascades and so it will hide your ip address. It is a Java application, open source and you can download it for free.
You may use JonDonym for free, but free mix cascades are restricted in some cases. Full speed and anonymisation features you will get only with a premium account.