Just making sure I understand your question correctly...
You have a new SD card in the phone, but when you mount it to your pc, you see the contents of another SD card?
You may not be clicking on the correct mass storage device... make sure you are opening the one for the phone.
If you want to delete them, *this will delete them forever, be careful* open my computer and then find the SD card, right click, and there should be an option to format it. As I said, this will remove EVERYTHING from your card. Make sure this is what you want.
If you'd like to move the pictures, all you would have to do is highlight all of the files, click copy, go to the destination SD card, and click paste.