I have an iPhone 5s and need to reset it?

My little cousin put a password on it and I didn't have touch ID and I didn't log into iCloud nor back the phone up yet since I just got it so. What do I do to reset the phone back to factory settings?

Put the iPhone in DFU mode and restore in iTunes. It will erase everything off of the device for security reasons.

Instructions here: https://www.theiphonewiki.com/wiki/DFU_Mode#DFU_Mode