You can easily remove or change the 6 digit passcode.  First you'll need to remove the profile that enforces the 6 digit passcode, then you can change your passcode to anything you want or remove it all together.

1)  In your iPhone/iPad settings tap on General

2)  Then scroll down and tap on Profiles

3)  Tap on CrewBuddy Passcode, then tap Remove

4)  Then you can go back to the first settings screen and tap Passcode
(or equivalent). There you can turn off the Passcode or change it to a 4 digit.