It's easy to restart your Fire TV. Just choose from these options:

Perform a power cycle:
• Disconnect the power cord from the back of the device or from the power outlet, and then plug it back in.

Use your remote: 
• Press and hold the Select User-added image and Play/Pause User-added image buttons at the same time, for about five seconds. 

Use the Fire TV menu:
• Select Settings > Device > Restart from the Fire TV menu.

That's it!