Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
1
It is not possible to use the current subscription payment for the Family subscription, the process to switch to the Family version is provided on this link, basically you would be charged for a new Family subscription and the remaining time on the personal subscription is converted to the Family version at a pro-rata percentage of 92%.
2
The alternative is to cancel your Personal subscription using the process on this link, then take out a new subscription to the Family version.
You should first check your eligibility to a refund using the process on this link.