SQL> create table t (col varchar2(100));

Table created.

SQL> insert into t values('My name is Michel');

1 row created.

SQL> commit;

Commit complete.

SQL> alter table t add (col2 clob);

Table altered.

SQL> update t set col2 = col;

1 row updated.

SQL> alter table t drop column col;

Table altered.

SQL> alter table t rename column col2 to col;

Table altered.

SQL> set lines 65
SQL> desc t
 Name                             Null?    Type
 -------------------------------- -------- ----------------------
 COL                                       CLOB

SQL> select * from t;
COL
-----------------------------------------------------------------
My name is Michel

1 row selected.

2. DBMS_REDEFINITION.CAN_REDEF_TABLE - used to check whether the table to be redefined (optional)

	BEGIN
	DBMS_REDEFINITION.CAN_REDEF_TABLE('SCOTT','SAMPLE1',dbms_redefinition.cons_use_rowid);
	END;
        /
3.DBMS_REDEFINITION.START_REDEF_TABLE - used to start the redefinition of the specfied table 
	 
	BEGIN
	DBMS_REDEFINITION.START_REDEF_TABLE('SCOTT', 'SAMPLE1','SAMPLE2','to_clob(col) col',dbms_redefinition.cons_use_rowid);
	END;
	/
4.DBMS_REDEFINITION.COPY_TABLE_DEPENDENTS - used to start the copy of the table 

	declare
	 error_count pls_integer := 0;
	BEGIN
	  dbms_redefinition.copy_table_dependents('SCOTT', 'SAMPLE1', 'SAMPLE2',
	                                          1, true,true,true,false,
	                                          error_count);
	
	  dbms_output.put_line('errors := ' || to_char(error_count));
	END;
	/
	
5.DBMS_REDEFINITION.SYNC_INTERIM_TABLE 

 	BEGIN 
	DBMS_REDEFINITION.SYNC_INTERIM_TABLE('SCOTT', 'SAMPLE1', 'SAMPLE2');
	END;
	/

6.DBMS_REDEFINITION.FINISH_REDEF_TABLE - finally finishing of the redefinition of table

	BEGIN
	DBMS_REDEFINITION.FINISH_REDEF_TABLE('SCOTT', 'SAMPLE1', 'SAMPLE2');
	END;
	/

TABLE sample1
 Name                                      Null?    Type                        
 ----------------------------------------- -------- ----------------------------
 COL                                                CLOB   

COL                                                 
----------------------------------------------------
abcdefghijklmnopqrstuvwxyz                          


1 row selected.