Which admin password are you talking about?
If the bios admin password - you could reset everything to default and should clear the password (though you'll likely need the pw to get into the menu to reset everything) - unless you find other instructions on clearing the cmos/bios settings... note - it is much harder to do with a laptop vs a desktop
If the windows admin account - I'd follow USAFRet's advice and do a format/reinstall of windows to clear everything out from the previous owner. In fact I'd recommend this even if it is the bios admin password that you are trying to clear.