When you open the App Store on your device, you are automatically notified if there are updates available for any of your installed applications. If you are unsure, you can click the Updates button on the bottom right.
You install updates the same way you install new applications. Simply click "Free" and then click "Install".
Sometimes shutting down your iPhone or iPod touch and restarting it can resolve problems with crashing applications. This is common to all applications, including Apple provided ones. It is a good first step in resolving the problem.
If your application continues to crash, please contact us. We strive to make our applications stable and will do whatever we can to resolve the problem. Any information you can give us to reproduce the problem will help greatly.