How do I leave one family and join another

See the article 'Leave [/Cancel] Family Sharing', click here--> http://support.apple.com/HT201081

- How to leave a family sharing group.

You need to be invited to the other or create one yourself.

Click on this link to learn how to 'Set up Family Sharing' --> https://support.apple.com/HT201088

Read the section: "Invite people to join your family"

Note special case: Move a child to another group using Family Sharing - https://support.apple.com/HT201080