When you upgrade to Windows 10, the older and exiting version remains on your computer, and if I recall correctly, you cab boot up with the older version.
Better way is to do a fresh Windows 7 re-install using your original CD or bootable USB. I created a bootable USB with WIndows 7 since the Acer Laptop does not gave a CD drive.
Thanks, I have an external drive, just have to find the discs!!