You can use SQL Plus:

Option 1) The simplest and most elegant Method

CREATE TABLE table_without_duplicates AS
SELECT DISTINCT *
FROM table_with_duplicates ;
COMMIT;

DROP TABLE table_with_duplicates ;
COMMIT;
RENAME TABLE table_without_duplicates table_with_duplicates;

Option 2) An Oracle-specific Method
For Oracle, this solution utilizes the unique rowid of each row in a table,
and removes all duplicate rows in a table:

DELETE FROM my_table t
WHERE EXISTS (
SELECT *
FROM my_table tt
WHERE t.rowid > tt.rowid
AND other criteria)

The rowid > part makes sure you take the first of the rows in the duplicate set...

HTH