> sudo -u postgres psql
psql (9.6.3)
Type "help" for help.

postgres=# \du
List of roles
Role name | Attributes | Member of
-----------------+-------------+-----------
<user-name> | Superuser | {}
: Create DB
postgres | Superuser | {}
: Create role
: Create DB

postgres=# alter role <user-name> superuser;
ALTER ROLE
postgres=#