need help in tuning update query

 Hi All,

can you help me in tuning this update query,

UPDATE   SIEBEL.CX_PPM_XM PPM

   SET   LAST_UPD = SYSDATE,

         MODIFICATION_NUM = MODIFICATION_NUM + 1,

         PPM.ACTUAL =

            (  SELECT   COUNT (IAL.SUBTYPE_CD) "Investigator Alert Letters"

                 FROM   SIEBEL.S_PTCL_SITE_LS SITE, SIEBEL.S_EVT_ACT IAL

                WHERE       PPM.SITE_ID = SITE.ROW_ID

                        AND IAL.CL_PTCL_ST_ID(+) = SITE.ROW_ID

                        AND IAL.SUBTYPE_CD = 'Document'

                        AND IAL.TODO_CD = 'Investigator Alert Letter'

                        AND IAL.X_LTR_SENT_DT IS NOT NULL

                        AND 1 = 1

             GROUP BY   SITE.ROW_ID)

 WHERE   PPM.NAME = 'Investigator Alert Letters'

         AND PPM.SITE_ID =