bought a used macbook from 2008

hello there. my name is malakai ward-hager. i bought a used macbook from 2008 at the santa cruz flea market, and it works but am having some technical difficulties. im automatically logged into the administrative user upon start of computer, but i cant edit any preferences or do ANYTHING technical without the darn password of the user who had this computer last (i dont think theyve used it in years because the software was totally outdated) how do i erase the old users and attain administrative status? plz help!!!