In most cases, you don't have to do anything. If your device is not set up to update your apps automatically, visit your app store and search for DECKEE. Your device will give you the option to "Update", if there is a new version available. If the app store is inviting you to "open" the app instead, this means you are already on the latest version.
For more information, please refer to the article How do I check what version of the app I have?