Before reinstalling make sure to back up or export your WhatsApp chats. To uninstall and reinstall WhatsApp on a Windows Phone:
- Swipe from right to left on the Start screen.
- Scroll down to WhatsApp, long press on the icon and select uninstall.
- Open Store and download the latest version.
- Follow the instructions on the screen to install WhatsApp.
Learn how to reinstall on: Android | iPhone | Nokia S40