You could always make a change to the email address directly in the db under the users table. If you would like to have an interface for the admin to do this you could use DataAssist to create a set of pages for administering the users. This would require you to run the DataAssist wizard and the pages would be created for you.
If you would like to allow the user's to change their email address you would need to modify the profile page to add in a text field for the email address then modify the update server behavior to bind this new email text field with the email column in your table. If you do this though you would want to add in an extra check to see if the new email address already has a record, otherwise you could end up with duplicate records and that would cause problems.
To check if the email has already been registered you would have a recordset that selects from the users table where the email address matches the one from your input, but only if the newly entered value differs from the current email address. Doing this would be a little custom and would require some hand coding.
