Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
The process to switch from one Microsoft 365 subscription to another version is provided on the link below.
To go from the Family edition to the Personal edition is explained in the 'Switch to a Microsoft 365 subscription with fewer features'.
Basically you need to cancel the existing subscription and cancel recurring billing on that subscription, when that subscription expires, you can then take out the new subscription
Provided you use the exact same Microsoft account on the new subscription, you will still have access to all your files and the same 1TB of OneDrive storage.