forgot administrator password

my daughter has an acer netbook running windows 7 starter, when i initially set it up for her i made it so that she would need the administrative password when ever she wanted to install anything, of course i only knew the password, well after not using the netbook for about 2 months ive forgotton the password and now the netbook can only be used under her account which is equivalent to a guest account, basically useless...is there anyway to override this? retrieve password? reset the o/s all together? i purchased the netbook as an open box item, so it came with no cd what so ever......