You can manage permissions of your Organization from its account page.
Here you can see who is the Owner and the Administrators of the Organization. You can transfer ownership to a different user and add or remove Administrators.
Administrators can do everything the owner can do e.g. create and delete projects, except delete the Organization.
You can see which users have access to your private projects and occupy your available seats. From here you can remove users which will remove them from all your projects, freeing up seats.
Here you can increase or decrease the number of seats for your Organization. This view is available if you have subscribed for an Organization plan.
The Owner of the Organization can delete the Organization from here. This will completely erase the account and all its projects. This action cannot be reversed.