Currently, there is no settings option in the Web Player. If your Chromebook is Google Play Store Enabled, you can download the Android version of the Spotify app from the Google Play Store. Using the Spotify app on your Chromebook, you'll be able to use Premium features such as downloading music for offline listening, and find settings.
If your Chromebook is not Google Play Store Enabled, your only option would be to use the Web Player.
Hope that helps!