When you first setup your Kindle you get to choose a name for your device which is always shown on the status bar. To change device name on Kindle Fire do as follows:
Note that, since we couldn't find a way to Change Kindle's name from the device's settings, you need to open a browser and do as follows:
1. Go to amazon.com and make sure to login with the same Amazon ID your device's been registered to.
2. On the top menu, tap the Your Account option to open a menu
3. Tap on the Manage Your Content and Devices option
4. Go to Your Devices tab and select the Device you want to change the name
5. Now you should see your device's current name, with a Edit button next to it
6. Tap the Edit button and set a new name as your Kindle's friendly name.