Amazon FireTV is a digital media player and networking device developed by Amazon. It can be used to stream high-definition media content to compatible television sets over WiFi. All you have to do is connect the Amazon FireTV device to your TV set using an HDMI cable or USB data cable and then you can configure or manage the FireTV console using a Bluetooth ready remote control or a USB keyboard. The device has features like voice search and allows installation of third party apps from Amazon app store. But if you want to install an app through APK file then it becomes really difficult without the help of any tools.
If you want more control of your FireTV stick and want to side-load apps using APK files then you can use the free Amazon FireTV Utility app. This utility runs in Windows machines and you have to connect your FireTV utility to your PC before you can perform all the modifications or side-load the apps.
Before you start using this utility, you should know that this utility also contains some functions to root your FireTV stick which basically voids the warranty instantly. So you should avoid using those functions unless you have a stick ready for experiments. Moreover the utility also warns about bricking your device if you attempt to root the device.
In order to side-load the apps, you have to choose the APK file and then click on the Side load 3rd Party Application button. The same section can be used to remove the app that you have already side-loaded on your FireTV stick previously. Among other things, you can use this utility to take screenshots, mount SD cards for special functions, install custom recovery image, and create backups of your data.
Conclusion: Whether you want to side-load the apps in your Amazon FireTV stick or you want to root the device for further customization, the Amazon FireTV Utility App gives you an easy graphical interface for all of these functions.
You can download Amazon FireTV Utility App from http://forum.xda-developers.com/showthread.php?t=2736774.