Modifying column size

I was wondering if anyone here knew of a way to modify the size of a column
in Postgres.  In Oracle, you can use the following syntax:

    alter table usrs modify passwd varchar2(32);    (For Postgres, I changed
the datatype to varchar)

But, when I try this in psql, it doesn't like the modify keyword.  I looked
in the documentation, and I found a doc note that someone else had tried
this as well to no avail.  Anybody know what is the correct syntax or if
this can even be done in Postgres?

Thanks!
--
Susan Lane
DPN, Incorporated
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