Can Users Update their Own Profile?

Yes. The [s2Member-Profile /] Shortcode makes it easy for users to edit/update their profile upon logging into your site. See: WordPress Dashboard s2Member General Options Profile Modifications for additional details and other options. Users can update their name, email address, password, and any custom fields that you've configured at Membership Levels that apply to a given user.

Can Administrators Update User Profiles?

Absolutely. Users can be edited/updated in various ways from your WordPress Dashboard at any time you like. See: WordPress Dashboard Users. Find (or search for) a specific user and click [Edit] to access their WordPress profile, along with all of the editable fields provided by s2Member.

See also: Customizing Your Login Welcome Page