Please follow these steps to delete and reinstall WhatsApp:
- Before you delete WhatsApp from your phone, you can use the Chat Backup feature to back up your messages.
- To reinstall WhatsApp:
- Touch and hold the WhatsApp icon on the Home Screen until the icons start to wiggle.
- Tap the x in the corner of the WhatsApp icon.
- Tap Delete to remove the application and all of its data.
- Press the Home button.
- Re-download WhatsApp from the App Store.
Learn how to reinstall WhatsApp on: Android | Windows Phone