This article explains how to restart a Kindle Paperwhite. It also explains how to force the process if your Kindle won't restart.
How to Reboot or Factory Reset an Amazon Kindle
If your Kindle Paperwhite is functioning normally, there are two ways to restart it. You can restart it through the menu options or you can force a restart by holding down the power button. Both methods have the exact same effect, so you can choose whichever you prefer.
Here's how to restart a Kindle Paperwhite using the menu options:
Swipe down from the top of the screen.