怎样改变表的属主。

I am sorry to think it maybe not alter the object schema.
But if you want the user 1 owned the user2 object,
you had two way:
  1)sql>  connect user1
    sql> create table tbname1
         as
          select * from user2.tbname;
  2) exp user1 file=... tables=(...,...)
      imp user2 file=... tables=(user1.tbname,...)