1. Find file pg_hba.conf. its here:
    C:\Program Files\PostgreSQL\9.1\data
  2. Open, and modifiy this line:
    #this for IPv4
    host all all 127.0.0.1/32 trust
    #this for IPv6
    host all all ::1/128 trust
  3. Restart your PC
  4. After that, login to database as postgres. Note that ‘postgres’ is root user. Now you won’t be asked for the password
  5. execute this query:
    ALTER USER postgres WITH PASSWORD ‘<your-new-password>’;
    example:
    ALTER USER postgres WITH PASSWORD ‘bayu’;