PL/SQL :: How To Check Record Exists Prior To Insert Statement

Using a cursor and loop method records are inserted into the header and line tables. How do I code the IF statement prior to the INSert statement such that Insert if record does not exist else Update the record. If the record for insert fails in the line, the same record should be deleted from the header table as well and transaction should rollback. The Ora version used is 11.2.0.2.

CURSOR C1 IS
        SELECT H.*
        FROM   rex_head_extract h
        WHERE  TRUNC(h.create_date) BETWEEN v_begin_date AND v_end_date;  
FOR I IN C1 (v_begin_date, v_end_date)
 
[Code]....

--- Need to perform a check if record exists here prior to insert     
             INSERT INTO tran_head
                 (TRAN_SEQ_NBR,        ORG_NUMBER,
                  STORE_NUMBER,        TRAN_DATE,

[Code]....