I don't think you are going to be able to upgrade via a network connection until you can connect. It is firmware not Elk RP version that fixes it. They use an older vulnerable version of TLS that Windows10 doesn't support out of the box. Do a google search against CT about the TLS issue, my solution was to change the port to 2101 but I already had it enabled for CQC.
You can see if 2101 is open with something like telnet or putty. If it is open, and you set 2101 in your account settings in ElkRP (not the M1XEP page, the front account settings page) then TLS isn't your problem. It doesn't use TLS at all.
If 2101 isn't open, you may be able to enable older TLS versions in windows or try something like windows XP if you have it available to get 2101 turned on or upgrade the firmware. Or you can try a serial connection to get things upgraded.
Edited by wuench, 25 November 2018 - 11:26 AM.