WhatApp has officially announced the version 2.12.90 on Nokia Symbian. Whatapps has been trying very hard to bring new features and updates on Nokia Symbian which is lacking behind as compare to Android and iOS operating devices.
Inorder to install the WhatsApp version 2.12.90 on Nokia Symbian you will need to uninstall the previous version of whatapp ie the whatapp which you are using on you device right now. But before installation that if ypu want to backup the chat you can do it.
Options->Settings->Chat History->Backup chat history.
Then go to whatsapp.com/nokia and download the WhatsApp 2.12.90 SIS file on your Nokia Symbian device. After download of the WhatsApp 2.12.90 SIS file is complete, you can install it on your device. Once the installation is complete, use your mobile phone number to get verified and restore the chat history.