How to change email on family sharing?

I'm not sure exatly what you mean by that.

Change your Apple ID - https://support.apple.com/HT202667 - "Follow these steps to change the email address that you use as your Apple ID."

"After you change your Apple ID email address or password, you might need to update your sign-in information with any Apple services you're using" Click on this link to read "What to do after [or before] you change your Apple ID email address or password" --> https://support.apple.com/HT204071

- You may wish to disable Settings > Find My before changing your information, change the information, then reactivate it with the new information.