Что-то делаете не так.
postgres=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+------------+------------+-----------------------
test | postgres | UTF8 | en_US.utf8 | en_US.utf8 |
postgres=# alter database test rename to test1;
ALTER DATABASE
postgres=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+------------+------------+-----------------------
test1 | postgres | UTF8 | en_US.utf8 | en_US.utf8 |
