You may need to remove contact details for a guardian, for example, if the email address is also being used on another user's profile.
Go to the Contact Details section of their profile and click on the contact detail.
Click Edit, then edit or delete the contact detail.
When editing a telephone number, keeping the names ticked in others who share this number will not delete the number off the other family members profiles. You would need to go to the other user's profiles to delete the number from there.