Solved! Go to Solution.
No need to switch accounts, you can just upgrade to Premium for Family at https://spotify.com/family 🙂
When you upgrade your subscription from regular Premium to Premium for Family, your next payment date will likely be a few days earlier than it had been. This is because of the difference between the price of Premium for Family and the regular Premium subscription you were on.
See your subscription page to keep an eye on your billing.