How to update a deal in self-hosted Bitrix24

In order to update a deal in bitrix24, this code can be used:

function OnAfterCrmDealAddHandler(&$arFields)
    {
     define("LOG_FILENAME", $_SERVER["DOCUMENT_ROOT"]."/custom_crm_log.txt");
        global $DB;
        $DB->StartTransaction();
        $arUpdateData = array(
               'COMMENTS' => "Hello world"
            );
        $deal = new CCrmDeal;
            if($deal->Update(
                $arFields['ID'],
                $arUpdateData,
                true,
                true,
                array('DISABLE_USER_FIELD_CHECK' => true))
            ) {
               AddMessage2Log("Successfully added", "custom_crm");
               $DB->Commit();
               $arErrors = array();
            }
            else
            {
               AddMessage2Log($deal->LAST_ERROR, "custom_crm");
               $DB->Rollback();
            }
    }