How do I change from an individual plan to a family plan?
If you already have an individual subscription, you can upgrade to the Family Plan without waiting for it to expire.
When you upgrade, Apple will issue you with a pro-rated refund for the unused time on your individual pass. This can take a few business days to show up.
If you wish to downgrade to an individual pass after purchasing a Family Plan, unfortunately they do not offer the pro-rating option. Instead of taking effect immediately like an upgrade does, when your Family Plan comes up for renewal you will instead be opted down into the Annual Pass.
The pro-rated refund is only given to the person who is upgrading. If you add a family member to your plan who already has their own subscription, they will not received a pro-rated refund.