If you have access to phpmyadmin you can replace password hash like:
for password: zaq!@WSX hash is
c1ce38227c8fc3aff37accf8fc31263e
in database table prefix_member
password row
PBBoard use MD5 hash so you can genarate hash for your new password on this site:
http://www.miraclesalad.com/webtools/md5.php
:)