ALTER TYPE changes the definition of an existing type. The only currently available capabilities are changing the owner and schema of a type.
You must own the type to use ALTER TYPE. To change the schema of a type, you must also have CREATE privilege on the new schema. To alter the owner, you must also be a direct or indirect member of the new owning role, and that role must have CREATE privilege on the type's schema. (These restrictions enforce that altering the owner doesn't do anything you couldn't do by dropping and recreating the type. However, a superuser can alter ownership of any type anyway.)
The name (possibly schema-qualified) of an existing type to alter.
The user name of the new owner of the type.
The new schema for the type.
To change the owner of the user-defined type email to joe:
ALTER TYPE email OWNER TO joe;
To change the schema of the user-defined type email to customers:
ALTER TYPE email SET SCHEMA customers;