Owners are not allowed to change the email's of other user's. This is because we can't verify the new email that is being entered.
To change the email of the user, kindly contact the user to update the email from their profile settings.
If you are logged in then follow these steps to change your email:
Hover over the user icon in the bottom left and click "My Profile".
Go to the email tab and proceed to enter your new email and follow the prompts in the page.