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 user list. Click on the Gear icon of the user you want to update role and choose Edit option.
From the Role section, choose the specific user group that want to move the user to.
Then, you can click the button Save Changes to update the user with the selected role.