Alter Table Auto_Increment

I have a table in my database and would like to modify the one column
that is already configured to be the PRIMARY KEY but I forgot to set
it for AUTO_INCREMENT. For some reason I can't find what the proper
command would be in the documentation and my commands from MySQL don't
appear to work properly in PostgreSQL:


sun=# \d blades
            Table "public.blades"
  Column  |         Type          | Modifiers
----------+-----------------------+-----------
 id       | integer               | not null
 ilom_ip  | character varying(15) |
 host_os  | character varying(50) |
 host_ip  | character varying(15) |
 hostname | character varying(50) |
 serial   | character varying(30) |
 gfe      | character varying(10) |
 admin    | character varying(50) |
Indexes:
    "blades_pkey" PRIMARY KEY, btree (id)

My command is not working so I don't know what I am doing wrong:

sun=# ALTER TABLE blades MODIFY int AUTO_INCREMENT;
ERROR:  syntax error at or near "MODIFY"
LINE 1: ALTER TABLE blades MODIFY int AUTO_INCREMENT;