Wired is probably better....if you can get it work correctly on your computer. However, there's nothing wrong with wireless as long as your drone model isn't prone to overheating.
@Junkman just make sure you have a reliable reasonably fast stable connection to the internet,
and to prevent overheating of the drone during updating, have a fan blowing over the drone to dissipate the heat build up inside the drone ,
i have always used WIFI to do updating ,and have never had any issues
There is another way with the DJI Go4 App.
Setup as if to Go flying. Go to the intro page.
Hold your finger on the three bar icon top right for about 10 seconds and release.
On release:
If you are successful an update firmware page will appear and you can update the firmware from the drop-down list.
The App will download the firmware .bin file to the cache on your device
and then extract and flash the firmware to your device.
To see a log file you can tap the dji icon on the intro page top left about six times in quick succession.
That said: I normally use a wired connection to a PC and a current version of Assistant 2.