I really like the Airspy HF+ SDR. Mine came with firmware 1.0 and I found it a bit of a puzzle to upgrade to the latest version 1.5 dated 2018-02-22.
First, you get the firmware (with flash bat file) not from the Download page but oddly right down the bottom of the Products page here. (I learned this from the excellent discussion group).
Second, you must be running Microsoft Windows to flash the firmware. This seems like a poor choice given that Airspy have made good choices in other areas such as open sourcing the drivers on GitHub here and providing a build of spyserver for the Raspberry Pi and similar ARM boards.
You can see what version of the firmware you have in the Source tab in SDR#.
Mine is now showing R1.5 but originally it was showing 1.0.
Because of a bug in 1.0 the simpler flash procedure outlined in the README doesn't work and you must open the box and short two contacts labelled Erase. You can see them here in this picture with the back off just below the shielded area (click image to enlarge):
I won't reproduce the README here as it might change but the process works and you see firmware update progress bars and as I said when you run SDR# it shows the new version.