To view your organization's administrators, go to Members and then click on the Administrators tab.

To add administrators, click on the Invite Administrator drop-down and then select Invite Administrator.

To provide some context, "root" administrators have more permissions than "default" administrators; for example, root administrators can add other administrators and make changes at the organization level, but default administrators cannot perform these actions. 

By default, additional administrators are default administrators, but they can be made root administrators if necessary. Having multiple root administrators is helpful when multiple people will be handling account management. 

Go to Members and then click on the Administrators tab. Then, select the administrator that you would like to make "root" (make sure their account is enabled first).

Then, click on the three dots (...) in the top right-hand corner and select Make Root Admin. 

To revoke administrator status, select Remove Admin. To revoke "root" status, click on the three dots (...) and select Remove Root Admin.