The link for the upgrade tool, as posted earlier, is http://static.tp-link.com/iotUpgradeTool_V1.0.zip
But, for my HS105, it would not find it after repeated scans. Then I happened to go back into Kasa and it had the HS105 listed as available. So I again tried updating the firmware within that and this time it found 1.4.0 instead of the 1.2.9 included in the Upgrade tool. Still "playing" with this thing... really shouldn't be this "quirky".