To change any of the details for an administrators account, head to the Administration section in the dashboard and then the People tab in the sidebar.
To change a users info, click the Edit button to the right of the users name.
In the view that appears, you can change the Name , Email and/or Password.
Here you can change the permissions this user should have. Tick all the boxes of the areas you'd like the user to have access to.
Here you can select which notifications/if any you'd like this administrator to receive.
Once you've made the required changes, hit the blue Save button. You'll then be taken back to the previous screen with the list of all people with admin accounts.