how can I change ios sdk?

I want to change my iOS SDK. I have ios 5 and xcode 4.2 but I have to decrease it to iOS 4.2 SDK because of my application. In developer.apple.com the xcode 4.1 with iOS 5 so it is not available. How can I find xcode 4.1 with ios sdk 4.2 or how can I setup the ios sdk 4.2 without download xcode again. If it is not possible can you give me a linq for download xcode 4.1 with ios sdk 4.2