How to behive if I remove password from postgres role

I wanted to install PostGIS Bundle so that it builds a sample spatial database, but got error - createdb: error: connection to server at "localhost" (::1), port 5432 failed: FATAL:  password authentication failed for user "postgres"

Then I altered role of postgres so, that password = NULL.

Now I am in situation that I can't run any postgres command.

What I must to do ?

Regards,

Raivo