Google started rolling out the new Android Auto earlier this month, and it's an overall improvement. You should have the updated interface already, but we've heard from a number of Android Auto users who haven't seen the update appear automatically. Luckily, there's a quick fix.
The new Android Auto should show up as a notification bubble on the old home screen when it's ready. Tap that, and you'll get a new notification instructing you to unplug and replug your phone to complete the upgrade. That's how it's supposed to happen, at least. For some reason, that notification isn't appearing for everyone. You can force the update in the app settings, though.
To toggle on the new Auto, open the Android Auto app on your phone and go to the settings. Right at the top, there's a toggle to "Try the new Android Auto." Presumably, the new interface will be the only one at some point, but for now, you still have to tap the notification or flip this switch.
- and everyone else