Apple announced the Xcode 5 Developer Preview today and I want to try it.
But before I download this, I want to know that what happen with my current version of Xcod
Short answer: Dont replace XCode 4! If you plan to deploy some app to appstore, you can't do it using Xcode 5 at this moment.
The best way is download the Xcode 5 version, unpack it and run the app on different folder (not application folder). You will stay with Xcode 4, and can run Xcode 5 separated (You don't need to 'install' xcode 5).