Disable/Remove Partitioning Option

[Thomasps]

But, for less down time you can use this method

Say you have a table

create table test2 (
OWNER          VARCHAR2(30),
OBJECT_NAME    VARCHAR2(128),
SUBOBJECT_NAME VARCHAR2(30),
OBJECT_ID      NUMBER,
DATA_OBJECT_ID NUMBER,
OBJECT_TYPE    VARCHAR2(18),
CREATED        DATE,
LAST_DDL_TIME  DATE,
TIMESTAMP      vARCHAR2(19),
STATUS         VARCHAR2(7),
TEMPORARY      VARCHAR2(1),
GENERATED      VARCHAR2(1),
SECONDARY      VARCHAR2(1))
partition by range (object_id)
(partition RANGE_1 values less than (15000),
 partition RANGE_2 values less than (20000),
 partition RANGE_3 values less than (MAXVALUE)
) enable row movement;

Create a temporary table while database is in restricted mode (To avoid simultaneous operations).

create table test3 nologging as select * from test2;
drop table test2;
rename test3 to test2;

Remember to keep Indexes, constraints, triggers and other associated objects. Validate after rebuilding. Export the table before doing the operation.