You can download the update directly on your device through the Windows Phone Store or by using the link which follows:
The WhatsApp for Windows Phone version 2.10 update has the following new features and improvements:
- Initiate voice calls from within the app
- Background API allows you to play music
- New smileys
- Fixed notifications for users
- Users can now see smileys on the double wide tile
- Fast resume (If the app is open and you click on the incoming notification it opens as fast as on Android)
- On start-up, it now asks if you want to back up your chat history. You can also do this through settings.
- Large images shown
WhatsApp Messenger is free for the first year of use, but requires a $0.99 per year subscription to continue using it. Considering that the result is a ad-free smooth messaging experience it probably is well worth its cost.