i got a pc from a person to use ubuntu.but that person has a pw for his user profile.I can't contact this guy and the terminal runs under his profile.all the online guides to reset the pw needed grub2 but system doesnt have it either. when i try to install grub2 terminal prompts for the user's pw.
PLEASE HELP ME OUT>>>thankyou.

First confirm whether your user account is added to /etc/sudoers. If not, add "admin" or "sudo" group as a secondary to your user account. Logoff and Login your account, now run the command #sudo passwd <user_name>. It will ask sudo password, type your password and it will ask you to enter new UNIX password for that user.