If you are upgrading to a new iPhone or other device, it is especially important to have a good backup of your data before you proceed. Here are some things to remember:
1. Before doing any upgrade, be SURE to backup your card data using the backup procedure within the app itself! Your data is NOT automatically backed up to the iCloud. You should be doing regular backups, but it is especially important now. See the writeups on Backup and Restore for full information.
2. If you are fortunate enough to have a second iOS device, this is an effective way to be sure that you have a good backup. See the writeup on Multiple Devices for full information.
3. If you do not have your data backed up to a second iOS device, it is highly recommended that you keep your old device after upgrading. This will give you time to use the app for a while on the new device and be sure that everything is working properly, before you lose control of device, which contains a known working copy of your data. After you have been using the new device for a month or two and are sure that everything is working properly, it should be safe to dispose of the old device.
4. Your cell phone provider or Apple will generally transfer all of your apps and data from the old device to the new one. However, the app does not always work correctly when this is done, and you card data may or may not be transferred correctly. You CANNOT rely upon this. If the app does not work correctly after the transfer, it is not difficult to delete the app and reinstall it. However, in doing this, all of your card data will be erased from the device and you will have to restore it from the backup. So please be absolutely sure that you have a good backup of your card data before upgrading to a new device.