A TTRS home subscription can be purchased as either an Individual plan (1 student) or a Family plan (2-6 students). The price in your local currency can be found here
To upgrade to a Family plan, visit the billing menu of your administrator account by tapping on your profile picture on the top right and then tapping on Subscription.
Select a plan and tap "Choose Plan" and follow instructions.
Note, if you are downgrading to an Individual plan, you will need to delete students from your account first. You can do this by visiting the Students menu.
Refunds for price adjustments related to plan changes may be processed on a case-by-case basis.