Databases are destroyed with the command DROP DATABASE:
Only the owner of the database (that is, the user that created it) can
drop the database. Dropping a database removes all objects that were
contained within the database. The destruction of a database cannot
be undone.
You cannot execute the DROP DATABASE command
while connected to the database to be dropped.
For convenience, there is also a shell program to drop databases:
(Unlike
createdb, it is not the default action to drop
the database with the current user name.)