Users with Administrator level permissions can elevate or remove permissions from any other level of user within their account.
To do this, you would click the "User" tab in the menu bar at the top of your screen:
Find the user you wish to manage permissions for and click the pencil to the right of their name:
Select the role you would like them to have from the dropdown and click "Update User".
There are three different permission levels for users within ThruText — Administrators, Moderators, and Message Senders. Click here for a full description of each of the three permission levels.