Once you have set your sub accounts, you can always change their settings with a few clicks. As you can see, you have a complete control over every profile:

Click on "Suspend" to interrupt momentarily the sub user's email credit.
Click on "Edit" to change the sub user's details (company info, address, etc.)
Click on "Limit" to put a cap to your sub user's monthly send capacity:

Click on "Delete" to cancel the sub account. The action is irreversible.