As default, the Air will be named by its serial number. Eg. "Air 100 008571" This is how it will appear in the app or when selecting it as your Airplay or Bluetooth speaker.
If you wish, you can rename the Air to something of your choice - for example, "Air Living Room", or "Ben's Air".
The easiest way to do this is from within the app, after you have set the Air up and connected it to your network.
To do this, go to Settings > Devices within the app and select the Air speaker that you wish to rename. Then press "Enter Web Page". This will open a webpage within the app where you can rename the Air.
Type the desired new name into the Airplay Device Name box, and press "Change Name". You will now get a "new settings were successfully applied" message, and your Air will have been renamed. You may need to close and restart the app to reconnect to your newly re-named Air speaker.