DROP TABLESPACE [ IF EXISTS ] tablespace_name
DROP TABLESPACE removes a tablespace from the system.
A tablespace can only be dropped by its owner or a superuser. The tablespace must be empty of all database objects before it can be dropped. It is possible that objects in other databases might still reside in the tablespace even if no objects in the current database are using the tablespace. Also, if the tablespace is listed in the temp_tablespaces setting of any active session, the DROP might fail due to temporary files residing in the tablespace.
DROP TABLESPACE cannot be executed inside a transaction block.
To remove tablespace mystuff from the system:
DROP TABLESPACE mystuff;
DROP TABLESPACE is a PostgreSQL extension.