Contact list connected to Kia Forte?

I connected my iPhone via USB into the Kia Forte I was driving. I had to download all my contacts on to the phone in order to make a Bluetooth call… Now I'm wondering, how can I remove all my contacts out of that car?

The car is not mine and I have to return it. I don't really want the next person to have all my contacts in there, and possibly even mix them up with theirs.

Yeah - never do that.