Changing Admin's password:
1) Edit
forum/setup_options.php and set
$admin_usr for new admin's login,
$admin_pwd for admin's password (you can also set encoded md5 hash for $admin_pwd - study in
Manual for more).
2) Log-in with the data saved in p.1 above as admin, go to Admin Panel (link appears at the bottom of the page), click on "Restore Admin's data in database".
You're finished!
This solution works for all versions of miniBB.