Disable simple passcode on iOS devices
Turn off the simple passcode option on your iPad, iPhone, iPod or iPad mini
Here's how you can turn off the simple passcode option on your iOS device. This will let you use more complex and secure passwords on your iPad, iPhone, iPad mini or iPod.
1. Go to Settings.
2. Go to General.
3. Go to Passcode Lock.
4. Toggle the Simple Passcode switch to the Off position.
For more, see the original article at the link below.