The Docker image is based on latest stable Fedora. It includes Spectrum 2 and also lot of 3rd-party backends you would have to compile or install yourself when not using Docker image. This includes:
Download the configuration file you chose into `/opt/spectrum2/configuration` directory you have created earlier and edit it as you want. Check the documentation and tutorials for configuration examples.
If you are using Docker bridge networking, you should configure your XMPP server to listen on the bridge IP address. Some XMPP servers listen only on 127.0.0.1 by default. Check [Prosody](https://prosody.im/doc/components) documentation for example config.
To upgrade Spectrum 2 container, you at first have to pull the updated Docker image, stop the current container, remove it and start it again using the new version of Docker image. It is very important to have all the Spectrum 2 data stored in the host system as described earlier in this document. Otherwise you won't be able to upgrade running container without loosing the data.