how can I change a btree index into a hash index?

I create a table like so:

create table types (
typeid integer unique not null,
typename varchar(255) unique not null
);

and I get the expected messages:

NOTICE:  CREATE TABLE / UNIQUE will create implicit index 'types_typeid_key' for table 'types'
NOTICE:  CREATE TABLE / UNIQUE will create implicit index 'types_typename_key' for table 'types

Since these are all unique things, and will only be tested for
equality, I am guessing that making a hash index will be better
than making a btree index.

1.  Exactly how do I do this?  I'm getting some hints that I should
     drop a constraint rather than drop an index, but I'm still
     not sure exactly what to type.

2.  Is this in general a good idea?  I will benchmark both ways
     but I'm interested in hearing any discussions regarding
     hashed indexing.

Many TIA!
Mark