Code:
SQL> create table xyz (company_name varchar2(20));

Table created.

SQL> create or replace trigger xyz_bia
  2  before insert or update on xyz
  3  for each row
  4  begin
  5     :new.company_name := upper(:new.company_name);
  6* end;
SQL> /

Trigger created.

SQL> commit;
SQL> insert into xyz values ('foobar');

1 row created.

SQL> commit;

Commit complete.

SQL> select * from xyz;

COMPANY_NAME
--------------------
FOOBAR

SQL>  insert into xyz values ('foobar2');

1 row created.

SQL> commit;

Commit complete.

SQL> select * from xyz;

COMPANY_NAME
--------------------
FOOBAR
FOOBAR2

SQL> update xyz set company_name = 'foobar1' where company_name = 'FOOBAR';

1 row updated.

SQL> commit;

Commit complete.

SQL> select * from xyz;

COMPANY_NAME
--------------------
FOOBAR1
FOOBAR2

SQL>