I just bought an Acer laptop from a friend and he does not remember his login password. Does anyone know how to retrieve or reset password?

Sorry but we cannot help you with this. This site is deeply involved with computer security and since we have no way of knowing if your friend stole that laptop or not we cannot help with lost or forgotten passwords. You need to return the laptop and get your money back. Tell your friend to take it to a shop with the original disks that came with the computer. The shop can verify identity and ownership, and reset the password. This is to protect you too - you do not want to be in possession of stolen properly, and sadly, laptops are easy targets for thieves. If he does not have the disks, be suspicious.