I'm not familiar with Lupu, but if it uses apt as package manager and uses same or similar repositories as Ubuntu, you can install it with:
Obviously, you must be connected to internet while installation. Better create a Live (persistent) USB and install it beforehand where you have internet access.
sudo apt-get install chntpw
Once installed, just take a look at its man page, it is really short and easy to follow. Main part of your interest is (example)-
However, if you need even more easy to use tool, try HBCD. It contains many NT password reset tools and some of them are pre-configured to auto-detect the SAM files.
ntfs-3g /dev/sda1 /media/win ; cd /media/win/WINDOWS/system32/config/
Mount the Windows file system and enters the directory \WINDOWS\system32\config where Windows stores the SAM database.
chntpw SAM system
Opens registry hives SAM and system and change administrator account. This will work even if the name has been changed or it has been localized (since different language versions of NT use different administrator names).
chntpw -l SAM
Lists the users defined in the SAM registry file.
(Besides NT password changers, it has hundreds of other utilities as well)
Also, if you need to 'Recover' an NT password, you can use Ophcrack live cd. Although the recovery process can take much longer and can even fail in case of long and complex passwords, while resetting is guaranteed and is done instantly.