1) Only install Off-The-Grid Maps (SD card) when you need it for a trip.
2) Move the files from your old SD card to the Off-The-Grid Maps memory card. We leave empty space on each card, so you can store and transfer personal data on it.
3) Move Off-The-Grid Maps to your old SD card or a bigger SD card.
For details on how to move files from one SD card to another read: "How to copy Off-The-Grid Maps to another memory card."