To change a user's role, log in as a user with the organization's owner. (Also, if there is only one owner, you cannot change the role of that owner.
1. Click on "SETTINGS" - "Organizations" in the header menu.
2. Click on the icon in the List of Affiliated Users column of the organization to which the user you wish to remove from the organization belongs.
3. A list of users who belong to the organization will be displayed.Click on the link of the user whose role you want to change.
4. Change the role and click the UPDATE button.
Please see here for the possible operations for each Role.