Well, There are two things you can do. You can try and contact the last owner of this laptop and try and get the password from them. Although, If you don't mind losing any data you can system restore your PC to how it was and then you will be able to make a new account on this laptop.
To system restore follow the instructions CAREFULLY below:
1.Turn on the laptop and when it boots it will appear with an Acer logo, When it says this mash F2 or F8 and a screen should appear. This is called the BIOS.
2.Now press the arrow keys until you reach a tab called "Boot" or something like that. When you have done that it should come up with about a list of 8 things. This is the booter order the PC will follow to boot the PC up successfully.
3.Now seeing as the Acer E1-571 is a little awkward to find the system restore you will have to switch something called the "Windows Boot Manager" with the "HDD". Now press F5/F6 until they are in the correct order. The HDD should be in boot order 1 and windows boot manager should be below that.
4.Now when you have finished doing that find something saying "Save settings and boot" or something like that. Now the PC will reboot. When the PC starts it will appear with a blue screen with something saying "Windows has had problems starting up". This is the Windows 8 Recovery window. Now Select "Advanced boot options" and find "Restore to factory defaults".
5.Now it will say things like are you sure and whatnot. Just agree to everything then the PC will now restore itself to how it came out of the factory(Hence the name Factory Defaults).
6.Wait for about 1-2 Hours depending on how big the HDD is.
7.Now your PC should let you recreate another account with your own password that you can't forget.