UPDATE EMPLOYEES tl
   set  T1.EMP_CODE=
                 SUBSTR(TL.EMP_CODE, 0, 2) || '01';

empcode  result
******   ****** 
1IMPOA   1I01 
1IPOKK   1I02      
2KPOIAA  2K01
2KPOOO   2K02
2Kg2O    2K03
3QOPP    3Q01 

	 CREATE TABLE EMPLOYEES
		 (
			 EMP_CODE VARCHAR2(15)
		 );

		 INSERT INTO EMPLOYEES VALUES('1IMPOA');-- EMP_CODE should be updated with 1IM01
		 INSERT INTO EMPLOYEES VALUES('1IPOKK');--EMP_CODE should be updated with 1IP01
		 INSERT INTO EMPLOYEES VALUES('2KPOIAA');--EMP_CODE should be updated with 2KP01
		 INSERT INTO EMPLOYEES VALUES('2KPOOO');--EMP_CODE should be updated with 2KP02
		 INSERT INTO EMPLOYEES VALUES('2Kg2O');--EMP_CODE should be updated with 2Kg01
		 INSERT INTO EMPLOYEES VALUES('3QOPP');--EMP_CODE should be updated with 3Q01
	         INSERT INTO EMPLOYEES VALUES('3QSPP');--EMP_CODE should be updated with 3Q02
	         INSERT INTO EMPLOYEES VALUES('3QSPP');--EMP_CODE should be updated with 3Q03
	         INSERT INTO EMPLOYEES VALUES('3QSPP');--EMP_CODE should be updated with 3Q04

How to change this update statement.
UPDATE EMPLOYEES tl
   set  T1.EMP_CODE= SUBSTR(TL.EMP_CODE, 0, 2) || '01' --this number should be increment;