If you're on WiFi 2.7.5 you need to stay with the 2.x series, 3.x and up is a different chipset. 2.8.2 seems stable and 2.9.1 is the latest and probably last update for this WiFi chipset I'm told. The WiFi firmware is pretty easy to update through the web interface.
For the main OpenEVSE firmware, 5.0.1 was the last stable version and now there is 7.1.3 which is pretty new. The mainboard firmware requires opening the unit and using a USB programmer to update.
The updates overall should provide better safety, stability, new features, etc.