To change your passcode:
First tap the "Settings" button on the main wallet page.
Then tap "Passcode and Touch ID".
You will be asked to enter your passcode on the following page.
Then, tap "Change Passcode".
From here, you will be able to enter a new passcode, or change the style of code by tapping "Passcode Options".
From here you can choose from a 4-digit numeric, or a custom alphanumeric option.
To enable or disable touch ID:
From the main "Passcode and Touch ID" page, you can tap the button to enable Touch ID. You will then be prompted for your biometric input (facial recognition or Touch ID)