If you are an administrator, click in the top right 'Settings (cog icon) > User Management' and click 'Edit' on the user you wish to update.
To change their name click on 'Edit Name'.
Update your own details
To update your own details go to the 'person' icon in the top right and choose 'Change My Details'. You can change your name, password and avatar. Your avatar is used in conversations in reports.