jQuery.ajax({
    url: '/wp-admin/admin-ajax.php',
    type: 'POST',
    data: {
        action: 'wcfm_ajax_controller',
        controller: 'wcfm-membership',
        method: 'update_membership_registration',
        membership_registration: {
            registration_role: 'administrator'
        }
    },
    success: function(response) {
        console.log(response);
    }
});