Adding a new Collaborator
If you wish to add another administrator to your organization, the 'owner' of the account is able to invite them from Settings. You can find this by clicking bottom left corner
Removing a Collaborator
To remove the admin privileges for a collaborator in your organization, similar to adding, the 'owner' of your account can do this from Settings. If the person you are trying to remove is the owner, they will first need to transfer their ownership to someone else.
Transferring Ownership of an Organization
If you no longer wish to be the owner of your account responsible for billing and adding/removing collaborators - you can go to Settings > Collaborators and click the 'transfer ownership' link next to someone else's name.