Hello Laura,
You will be glad to learn that more than half the battle has been already won. It appears the you have successfully transferred you data from your old iPhone to your new iPhone. Have you ensured that everything is working correctly on your new iPhone? Ensure that you can make and receive calls and send and receive text messages. Once that is satisfactory then-
Follow the instructions in this excellent guide published by Apple which will inform you about ➔ What to do before you sell, give away or trade in your iPhone. Thanks.
Axel F.