By default iOS devices will automatically update apps without any action from you. If you have disabled automatic updates, then you can, and should, update the app manually. On your iPad, iPhone or iPod touch, simply click on the App Store icon, click "Updates" on the bottom right of the screen and find the Echo Meter Touch or Song Sleuth app in the list. Click "UPDATE" to the right of the app's icon.
Note that you will need to be able to connect to the internet to download the update. You may also need to know the iTunes password for the device. If you would like a visual demonstration, watch the video here.