As an account administrator, you can update the name and permissions of existing users. You cannot change another user's password however.
If you are an administrator, go to 'Settings > 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.