Once you get to the CLI via SSh, this article is immensley helpful for upgrading firmware from it.
https://help.ubnt.com/hc/en-us/articles/205146110-EdgeMAX-Upgrading-EdgeOS-firmware
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In windows you can use putty as a telnet client looks like if your on mac do this:
http://www.unixnewbie.org/putty-equivalent-for-mac-os-x/