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