Amazon is looking to better your experience with the Fire Phone with this new update. Version 3.5.1 includes improved battery life; Quick Switch feature that lets you double press the home button to switch between or shut down apps; and the ability to create folders of apps or content on the app grid. You can now also pin your favorite apps on the home carousel and delete emails directly from the home screen. You also get the ability to create lenticular photos with 11 still images instead of 3. Here’s a link that lists down the new features and how users can gain access to the latest update.
Source: Android Central