An error has occurred downloading the update
I am selling my old MacBook Pro mid 2012 laptop. I followed the directions to erase the hard drive and reinstall found here (https://support.apple.com/en-us/HT208496). When I reinstalled the MacOS it went to what I assume was the original OS of the machine which is x. I was running macOS Sierra 10.12.6 and I would like to put it back to that. However, when I go to update the OS to get back to Sierra I do not see it as an option. It has "software update". When I click "update" it says "An error has occurred An error occurred while downloading the updates (102) I can't imagine why it won't let me go back to Sierra as I was just on that when I reinstalled. Any help would be greatly appreciated!
It's also taking a really, really long time to do a restart which is not normal for my machine. Any help on why that is?
MacBook Pro (13-inch mid 2012)
Processor 2.9GHz intel core i7
Memory 16 GB 1600 MHz DDR3
Graphics
currently since reinstall version 10.8.5
MacBook Pro 13″, macOS 10.12