SharePoint UPS Change SharePoint Active Directory to SharePoint Profile Synchronization

Hello together

We want change the Settings of our User Profile Service Application from SharePoint Active Directroy Import to SharePoint Profile Synchronization. We don't like lose the information already synchronized or the already existing profiles.

1. Is there anything to consider?
2. If we delete the existing synchronization connection, will the existing profiles  or the 3 UPS databases be deleted or reseted? 

Thank you

Kader