postgresql db account

What is the default pw for the postgresql db account?
Is it a correct management practice to change this pw?

template1=# select * from pg_user;
  usename   | usesysid | usecreatedb | usesuper | usecatupd |  passwd  | valuntil | useconfig
------------+----------+-------------+----------+-----------+----------+----------+-----------
 postgresql |       10 | t           | t        | t         | ******** |          |