There should be an option in the phones gallery to do this. If it doesn't allow it (as some models don't) you can always plug the phone into a computer (via USB) and move the images over to the SD card. You can also, then, save copies onto the computer, so you don't lose them if something happens to the phone or the card.
You should, however, be able to get the images off the phone at the store, on one of their devices, without moving them over to the card.