As an admin or coach, you can't always change a member's email. But they can do it themselves on their profil in some cases.
If a player of your team has not activated his account after your invitation, then the email of the player is not shown on the team roster or on his profile page. You can easily modify the email address and then send a new invitation to join the team to the new email address.
If a player has already activated his account and joins the team afterwards, the email address is shown on the team roster and on his profile page. You can't change this email anymore. The email might be used for other teams, so it can't be changed. If a player wants to change their email address, they must log in using this email and password, and change the email in their account settings.