Updating to macOS High Sierra Download doesn't finish
Given the context of your question, it's unclear if you re-downloaded the installer from the App Store after the first failure or if you ran the upgrade application again. Yes, your computer is supported for the High Sierra update. I have a few suggestions:


Delete the upgrade application (go to the Finder and delete it).
Re-download the upgrade application from the App Store.
Run the application again.


If the problem persists, the solution will probably involve something more drastic. If you have an available flash drive, try making a bootable flash drive installer. Restart and hold (Option) and select the bootable USB disk and hit enter. Proceed through the install process. Notify us of the result and we'll proceed from there :)

Good luck ;)