Thank you for reaching out here in the Community!
When you join a Family plan with your existing Spotify account, all subsequent payments on your account will be made by the plan’s manager (the person who started the plan).
If you had Premium direct with Spotify, your billing switches automatically - you don't need to cancel anything.
However, if your Premium Individual plan was associated with a partner, you need to cancel with them.
For more details on Premium Family, make sure to check out this support article.
I hope you'll find this helpful!
Help others find this answer and click "Accept as Solution".
If you appreciate my answer, maybe give me a Like.
Note: I'm not a Spotify employee.