If your iPhone is lost or stolen, you can erase it remotely. Sign in to Find My iPhone and select the device. Tap to see your options.
Tap Erase iPhone. If your iPhone is online, remote erase begins within seconds. If your iPhone is offline, the erase will begin next time it’s online.
Note: If you erase your iPhone, you won't be able to use Find My iPhone to locate or protect it, but your Apple ID and password will be required to reactivate it. More: Find My iPhone overview