Some clients need the option to restrict or allow their users to edit their account detail information.
The setting for this is found on the User group panel, click on the settings tab of the usergroup you want to modify. You will see the User Settings section, "Block Editing User Information" set this option to No, to allow users to make changes to their user detail.
Some fields are not editable unless the user has administrative access. These fields are their username, email notification settings, user group assignment, approving manager if applicable and any custom fields that may be set on the user level.