In the backend administrator area, navigate to:
Site > User Management
Scroll down until you can find the user that you need to modify. The filters can also be used to help filter down the view and search for the user’s account. Once you have found the user, click on their name to modify their details.
Change the details that are required and hit save in the top right corner of your screen. Test the account by either logging in to the front end of the site or the backend of the site if they are a site administrator.