To change the roles of a user, you must be an administrator.
Perform the following:
In the bottom of the navigation pane, click Settings.
Click the Users tab.
A list of all users appears. You can see the roles of each user in column Roles.
Click the user whose roles you want to change.
Select or deselect the roles that you give or take from the user.
The roles are applied instantly.
Navigate back to the Users page.