i need to change my family sharing organizer for he is no longer in the family

Having a young child in the family might be the reason why you can't disband. In that case contact Apple.

iTunes and App Stores support --> https://support.apple.com/en-euro/itunes-contact

or:

Contact - Official Apple Support --> https://support.apple.com/contact

or:

Contact Apple for support and service --> "See a list of Apple phone numbers around the world." - https://support.apple.com/HT201232

I think the only way to do this is to disband the family sharing group and set it up again.

Leave [/Cancel] Family Sharing - http://support.apple.com/HT201081