Additionally, if you want to change from 6 digit passcode to something else do the following:
On iOS 11
Go to Settings
Touch ID & Passcode
Enter your passcode
Change Passcode
Enter your passcode
Click Passcode Options and get:
Custom Alphanumeric Code
or
Custom Numeric Code
or
4-Digit Numeric Code
or
Cancel
Additionally, if you want to change from 6 digit passcode to something else do the following:
On iOS 11
Go to Settings
Touch ID & Passcode
Enter your passcode
Change Passcode
Enter your passcode
Click Passcode Options and get:
Custom Alphanumeric Code
or
Custom Numeric Code
or
4-Digit Numeric Code
or
Cancel