As a program administrator, you are the only one that can change a user's email address in the program.
Do change the email address, follow the below steps:
Go to ACCOUNT
Select ADMIN HUB
Select USERS
Type in the users name so it brings it up in the search. Once that User has appeared, select EDIT (towards the right hand side of their name is where it will appear)
Edit their email address to the new one
Tick NOTIFY USER underneath where the email address box is
Scroll down to the bottom of the page and select UPDATE USER