s2Member allows any user with the create_users WordPress Capability (which, by default, is only WordPress Administrators; see WordPress Codex: Roles and Capabilities) to access any of the s2Member plugin options.

If you want more control over who can manage the s2Member Plugin Options, you can create an MU-Plugin that uses a filter to prevent the s2Member menu options from being displayed.

       add_filter('ws_plugin__s2member_during_add_admin_options_create_menu_items', '__return_false');

In this example, you could change SOMETHING to any WordPress Capability (see WordPress Codex). You could also customize this code to use a different conditional that checks for something else that lets you control access to who can manage the s2Member Plugin Options.