Before your users may change their settings you must allow them to change their LDAP data.

This can be done by adding an ACL to your slapd.conf which looks like this:

access to

attrs=mail,sn,givenName,telephoneNumber,mobile,facsimileTelephoneNumber,street,postalAddress,postOfficeBox,postalCode,password

by self write

If you do not want them to change all attributes then reduce the list to fit your needs.