Setting iPhone lock screen protects your data from being stolen and protects your device from intended access or some unintended actions like a slide to the unlocked screen. The Apple password normally would consist of a 4 digit number, a strong alpha-numeric password, or the Apple's Touch ID fingerprint on iPhone 5s/6/6 Plus. Until you enter the correct passcode to open the Lock screen, there's very little you can do with iPhone. With iOS 7 and iOS 8, Apple has made Notification Center, Calendar and Camera available from the lock screen. Changing the passcode regularly is a sensible security measure to prevent unauthorized access to your iPhone. You can reset the passcode through the Apple iPhone's Settings menu.
Instruction: How to Reset Apple Password
Go to Settings on your iPhone
Tap “Touch ID & Passcode”
Click “Change Passcode”
Enter your old passcode > Enter your new passcode > Re-enter your new passcode
Note: Resetting passcodes on your iPad and iPod touch would be the same as resetting passcode on iPhone.
Now, you have reset your iPhone password successfully. You can press the lock key and then it will ask you for your passcode before you can enter your control center with new passcode for a check.
You can also set up a strong alpha-numeric password and open “Erase Data”. You can go to Settings > Touch ID & Passcode and turn “Erase Data” on. If users have entered wrong password more than ten times, the system will erase all of your data stored on your iPhone automatically. This is a good way to protect your data from being stolen. You can also set up the applications including Voice Dial, Siri, Control Center so that they can be allowed to be accessed when your device is locked.
Another good way to protect your data is backing up them on PC with iPhone Transfer. If you accidentally delete data on your iPhone or lose your iPhone, you can recover them by iPhone Data Recovery.