Remove older assistant.
Connect to FC with v1.50 software.
It will connect but lower right corner will remain "unconnected" and it's ok.
on "info" screen click "flight controller upgrade", click view version and hit upgrade. You need to be connected to internet.
FC upgrade should be done and now software shows "connected" in lower right corner.
Remove battery and usb cable.
Connect usb to GPS puck. -If your gps is v1 with neo6m chip do not upgrade. it will not work. This upgrade is just for neo7 chips-
on "info" screen click "gps module upgrade". Click "view version" then hit upgrade.
Remove usb and connect it to FC again.
Now in info tab you should see gps version 1.20 and FC version 1.40
FC basically reverts everything back to default after upgrade. You should do calibrations and settings all over again.