how do you change password from 6 to 4 digits?

Go to Settings>Passcode & Touch ID. You will have to enter your passcode to enter there. Then go to Change Passcode. That will require you to enter your passcode again. It will then default to 6-digit, or tap on Passcode options and get the other options.

Thank you so much. I didn't see where it says options the 2nd time u sign in . I did it once on my iPhone .

thanks again

You're welcome.