Change from shared Apple ID to Family sharing

There may be some data loss, but you can minimize it. If syncing photos with iCloud, ensure Optimization is turned off in Settings/Your Name/iCloud/Photos and/or in Photos/Preferences/iCloud. Then make sure full resolution photos are on the device/computer. When signing out of iCloud, if asked whether you want to retain data, choose yes. Messages conversations will be lost if they are addressed to the ID. See the article below for other places that the old ID should be removed. See Winston Churchill's response in the below discussion. Also set up Family Sharing to keep access to your apps/purchases. 

Apple ID – Create

How to transfer all files from one iCloud account to another

 Apple ID email address or password - What to do after you change

Family Sharing lets you share purchases : Family Sharing - Apple Support and Share App Store, iTunes Store, and Apple Books purchases with Family Sharing - Apple Support