orclz>
orclz> create table parts(c1 number) partition by range (c1)
  2  (partition p1 values less than (10), partition p2 values less than (20));

Table created.

orclz>
orclz> alter table parts modify partition by range (c1)
  2  (partition p1 values less than (5), partition p2 values less than (10),
  3  partition p3 values less than (15), partition p4 values less than (20));

Table altered.

orclz>