Mac – Is it safe to remove the “Install Xcode” application after installation

I know it's a bit confusing, but you didn't actually install Xcode 4. What you did was installing the Xcode 4 installer. So what you got to do is:

1. Open the Install Xcode-app located in your launchpad.
2. Make sure iTunes is closed, this is necessary, and the installer won't check for this.
3. Finalize the setup (well, Lion will do this for you, just press the buttons).
4. Optionally, restart your Mac.
5. Optionally, remove the Install Xcode-app.

It'll probably prompt you that it's moving your existing Developer-folder to Developer Old so it can install Xcode 4.1 to /Developer/.

Can I safely remove old versions of Xcode which are using a lot of space?

Yes.

If I can, what should I do?

Run:

sudo <Xcode>/Library/uninstall-devtools --mode=all

Where <Xcode> is usually /Developer but can sometimes be ~/Developer depending on whether you installed it with sudo privileges or not.

Once you've run that script you can just move /Developer or ~/Developer to the trash, you don't need it any more.

You can can get more details about uninstalling by reading the About Xcode.pdf document in your directory.

If you also have a /Developer-old directory you can just move that to the trash.