This article will show you how to find and change the user's role. This assumes you are already logged in as the Admin user and are logged into the AdminCP.
On the slide of the Menu bar, go to Members, then select Browse
You will be redirected to the Browser page and can see the users lists from the Options field, click on the Gear and choose Edit
From the Role section, choose the specific user group that wants to move the user to.
...
Then, you can click the button Save
...
Changes to update user with the selected role.