Unlike adding a completely new user, you can also make a few changes to the details of the existing user accounts. It is not possible to change the username or the email ID of the existing user, as they are unique to every user. 

Apart from the user email ID and the username, any other changes that need to be made to the user accounts can be made by going to the Users section in the Eligibility File, finding the specific user row, choose the EDIT option against that row and update the needed details in the right place. Once all the details are entered, click on the UPDATE option to have the details updated to the user account.