I need help removing obsolete, unsupported antivirus?

My mum gave me her old laptop, I put the new AVG 8.0 on it and it says there is another antivirus on the computer so won't work properly, turns out the other antivirus is VET antivirus 2004 which has been discontinued and there is no support for it, when uninstalling it won't uninstall as one of the files is missing does anyone have a tool or program I can run that will remove it?