How can I permanently remove my iPhone 5 contacts and SMS?

I bought myself a new iPhone 5s yesterday, and I want to resell my old iPhone 5 to my friend, but there are so many phone numbers and SMS inside it, they are important and private as for me, I know someone can completely restore it using a recovery tool even I have deleted all on my iPhone. Therefor, is it possible to permanently remove my iPhone 5 contacts and SMS, anyone who can help? Thanks!