data conversion from char(4) data to char(2)

I have table called packagelines contains 3220 records
SQL> desc packagelines;
Name Null? Type
----------------------------------------- -------- --------------
CORP NOT NULL NUMBER(2)
PKG NOT NULL CHAR(2)
PKGSTOP NOT NULL CHAR(6)
LINE NOT NULL CHAR(4)
RCODE NOT NULL CHAR(2)

Now i want to reduce the size of a column LINE CHAR(4) to CHAR(2).How can i do it.
only two character data is present in the column LINE

Think you'd have to create a new table with the char(2) column and then insert using rtrim. Then drop the old table and rename the newly created one e.g.

SQL> create table t3 (col1 char(4));

Table created.

SQL> create table t4 (col1 char(2));

Table created.

SQL> insert into t3 values ('AA');

1 row created.

SQL> commit;

Commit complete.

SQL> insert into t4 (select rtrim(col1,' ') from t3);

1 row created.

SQL> commit;

Commit complete.

SQL> select * from t4;

CO
--
AA