Can you upgrade number of players in Minecraft windows 10/PE realms?

If I buy a subscription for 2 friends, can I upgrade to 10 friends and vice versa? If so, does it have to be between billing cycles?

I don't want to have to create a new world when I find more friends or pay more than I have to.

Solution 1:

If you want to change the size (go from 2 users to 10, or from 10 to 2), you will have to cancel the subscription to the Realm, wait until the remaining days expire, and then renew the Realm in the desired size.

https://help.mojang.com/customer/portal/articles/2461089#tier

You could also probably backup/download your world, buy a new realm and upload/import the backup to a new realm that you buy.