As an admin, you can change the amount of seats on your Team subscription at any time.
If you add additional seats to your Team subscription, they'll be prorated for the remainder of your billing cycle. You’ll be charged for the full seat as soon as your billing cycle begins again.
If you add a seat and it remains empty, you will still be charged.
You won't receive any prorated refunds for removing seats from your Team. Once your billing cycle starts over, you’ll no longer be charged for the seat(s).