Hello and welcome to Tom's Hardware Forums.
It's actually against the Forum Rules even to ask for password removal help let alone give advice on it and as de5_roy says. it can't be done. If the seller didn't let you have it cheaply on the basis it didn't work, and If it's a BIOS password take dontqqnub's advice.
If it's only a Windows system password, remove the hard disk, buy another and install a new system. Many Linux systems are free of charge if you can't afford Windows - they're just as good and in many cases, far better anyway.