How to upgrade to a newer version of Opera, or migrate your preferences to an Opera installation on a different device.
These notes attempt to consider several different but similar cases. Perhaps you want to upgrade to a newer version of Opera. Perhaps in doing so you want to retain your old settings. Perhaps you have Opera as you like it on one computer and want to replicate your preferences in a new installation of Opera on a different device, perhaps on a different platform.
The simplest case is upgrading your current version to a newer one. The installer first looks for an existing Opera installation. On Linux that would be at ~/.opera/, and on Portable Apps at %drive%\PortableApps\OperaPortable\. If the installer finds a previous installation, it performs an upgrade; if not, it performs a clean install, creating the installation directory given above.
TODO: Finish this article.