There is software out there that can recover deleted photos. I think it was/is made by sandisc.
When you create any computer file (which is what a digital picture is) it writes the data on the disc and then creates a pointer in an index. To find file xyx.jpg the system will go to the index, find the pointer and thus find the file. All that happens when you delete a file is that the index item gets deleted; the data is still there.
So long as you have the software and have tried it out and understand it you can delete with impunity. Immediately afterwards, take that card out of the camera (so the data is preserved) and put a new one in. Wen you get home retrieve the pictures.