In the app, go to Settings, and under Amazon Echo, click your Echo (whatever you named it)
That will bring up information. Close to the bottom of that page, you'll see this:
Echo software version 2530.
Right now, mine is at 2530. I don't think we've gotten any other updates since this one. There's supposed to be another update around the middle of July which will (hopefully) fix the stuttering of Prime music playback but sometimes we actually don't know what the updates do.
If you have your preferences set to receive emails from Amazon
In the Amazon website, go to Your Account. Look at the big left hand side headings until you see Message Center.
Under message center, see Notification Settings and look for Email preferences & notifications.
Click that link. That brings you to a page where you can select which emails you want to receive.
Make sure you have Amazon Echo and Kindle Devices & Accessories. I also have Surveys & Feedback checked. When there's an update, usually Amazon will send out an email telling us about the new features.
Hope this helps.