Where are the instructions for this process
How do I upgrade my current Xcode 14.3.1 to version 15.2?
I would recommend to go to the App Store and download the latest Xcode available. If you want to target a version you may find it sometimes in the developer's website downloads, but not all versions available, you should always try to run the latest from the app store available for your computer.
Hope this helps
Albert Pascual Worldwide Developer Relations.