How to rollback a sql

I would like to know how to make the pgsql system not doing the auto
commit and let me have time to do the roll back.

Just start by executing the query "BEGIN" and then it won't commit until you
execute the query "COMMIT".

ex:
=> BEGIN;
=> [ more queries here]
=> COMMIT;

or
=> BEGIN;
=> [more queries]
=> ROLLBACK;

Regards,
Jeff