1 - Remove/Unistall old Aero and All WhatsApp versions from your device.
2 - Delete the WhatsApp folder. If you have important data in it, you can move this folder to another location.
3 - Install WhatsApp Aero on your device. It is recommended to use WP Aero in the original package name. Touch me (You need to uninstall Original WhatsApp to install this) if you don't know where to download.
4 - Verify your number. Never restore old backups (chats) (backups from V7.96 and earlier) in new versions (V7.98 and later). Installation from scratch is recommended, restoring backups(chats) is very risky.
5 - If the WP Aero application issues a warning in the form of Google Play Services during initial setup, simply press the back button of your device.