1) Create a database backup

2) Execute following commands

INSERT INTO `configuration` (`configuration_key`, `configuration_value`, `configuration_group_id`, `sort_order`, `last_modified`, `date_added`, `use_function`, `set_function`)
VALUES ('CLEVERREACH_API_CLIENT_ID', '', '17', '16', NULL, now(), NULL, NULL);

INSERT INTO `configuration` (`configuration_key`, `configuration_value`, `configuration_group_id`, `sort_order`, `last_modified`, `date_added`, `use_function`, `set_function`)
VALUES ('CLEVERREACH_API_USERNAME', '', '17', '17', NULL, now(), NULL, NULL);

INSERT INTO `configuration` (`configuration_key`, `configuration_value`, `configuration_group_id`, `sort_order`, `last_modified`, `date_added`, `use_function`, `set_function`)
VALUES ('CLEVERREACH_API_PASSWORD', '', '17', '18', NULL, now(), NULL, NULL);

INSERT INTO `configuration` (`configuration_key`, `configuration_value`, `configuration_group_id`, `sort_order`, `last_modified`, `date_added`, `use_function`, `set_function`)
VALUES ('CLEVERREACH_API_IMPORT_SUBSCRIBERS', 'true', '17', '19', NULL, now(), NULL, 'xtc_cfg_select_option(array(\'true\', \'false\'),');

INSERT INTO `configuration` (`configuration_key`, `configuration_value`, `configuration_group_id`, `sort_order`, `last_modified`, `date_added`, `use_function`, `set_function`)
VALUES ('CLEVERREACH_API_IMPORT_BUYERS', 'false', '17', '20', NULL, now(), NULL, 'xtc_cfg_select_option(array(\'true\', \'false\'),');

3) Upload new files to the shop root from the folder "new_files"

4) Make following changes to the existing files

In lang/english/admin/configuration.php   

define('CLEVERREACH_API_CLIENT_ID_TITLE', 'Cleverreach Client ID');
define('CLEVERREACH_API_CLIENT_ID_DESC', '');
define('CLEVERREACH_API_USERNAME_TITLE', 'Cleverreach Username');
define('CLEVERREACH_API_USERNAME_DESC', '');
define('CLEVERREACH_API_PASSWORD_TITLE', 'Cleverreach Password');
define('CLEVERREACH_API_PASSWORD_DESC', '');
define('CLEVERREACH_API_IMPORT_SUBSCRIBERS_TITLE', 'Cleverreach Import newsletter subscribers');
define('CLEVERREACH_API_IMPORT_SUBSCRIBERS_DESC', '');
define('CLEVERREACH_API_IMPORT_BUYERS_TITLE', 'Cleverreach Import buyers');
define('CLEVERREACH_API_IMPORT_BUYERS_DESC', '');


AND  


lang/german/admin/configuration.php  add before the closing ?> tag

define('CLEVERREACH_API_CLIENT_ID_TITLE', 'Cleverreach Client ID');
define('CLEVERREACH_API_CLIENT_ID_DESC', '');
define('CLEVERREACH_API_USERNAME_TITLE', 'Cleverreach Username');
define('CLEVERREACH_API_USERNAME_DESC', '');
define('CLEVERREACH_API_PASSWORD_TITLE', 'Cleverreach Password');
define('CLEVERREACH_API_PASSWORD_DESC', '');
define('CLEVERREACH_API_IMPORT_SUBSCRIBERS_TITLE', 'Cleverreach Importiere Newsletterabonnenten');
define('CLEVERREACH_API_IMPORT_SUBSCRIBERS_DESC', '');
define('CLEVERREACH_API_IMPORT_BUYERS_TITLE', 'Cleverreach Importiere K&auml;ufer');
define('CLEVERREACH_API_IMPORT_BUYERS_DESC', '');
