Once the application is installed, it will check if there is a newer version every time it is launched.
If a new version is available, you will be notified and will be able to download the new version. To do that, go to Settings and click on Update.
Have in mind that software upgrades cannot be done over 3G channels in order to avoid abnormal data consumption. Please make sure you have an alternative connection to the Internet, such as Wi-Fi.