Do you mean Family Sharing or do you mean Apple Music?
Leave [/Cancel] Family Sharing - http://support.apple.com/HT201081 - How to leave a family sharing group
Manage your Apple Music membership on your iPhone, iPad, iPod touch, Mac, PC, or Apple TV - https://support.apple.com/HT204939 - "Learn how to cancel your membership, change from an Individual to a Family or Student membership type, or join an existing Family Membership."