[xwiki-users] Modifying the e-mail in a user profile.

Hi, I would like to consult and above all to modify the e-mails of some users profiles that I have created a long time ago. I try to change them via the Users menu in XWiki Administration menu, however the e-mail is not available among the fields that can be edited in the user profile form (nor advanced nor simple form). How can I do ? Thanks, S.A