You add them just like any other user! Click on People then on Users. From there, click the blue Add User button on the top right. Fill in their information and change the Role from Learner to Admin. Once that’s done, click Create on the bottom. Keep in mind that the amount of admins you have are limited depending on the plan that you are currently on.
To remove an Administrator, simply click on People, then Users, and click on the red X beside their name under Quick Actions.