How to upgrade Xcode 4 to 4.1? After upgrading to Lion, I am getting a launch error from Xcode 4 saying it requires Snow Leopard. I see 4.1 is now a free app for Lion in the App Store, but it doesn't show up in Software Update.

If I install it from the App Store will it upgrade 4.0 or live side-by-side?

Or, do I have to uninstall Xcode first if I only want 4.1?
You need to install XCode 4.1 from the app store, which will replace XCode 4.0 with 4.1.

When updating XCode to 4.1 you will get a message to quit iTunes to continue the installation. The installation is actually waiting for iTunesHelper process to be terminated. You can terminate the iTunesHelper process using activity monitor.

On my Mac the upgrade to XCode 4.1 failed. So I needed to uninstall XCode 4.0 first.