Yes we know.... ha-ha.. been like that all the time, Autel don't seem to want to do anything about it to make it easier, just having which version of FW would be the answer rather than having to decipher through each individual FW version from their site... plain weird...
You should get a message on the controller telling you there is an update available, follow instructions and it should download to the controller, re-start everything and it should install to everything... notice I say should do, sometimes it works, sometimes it doesn't.. this is why they give you the SD card option... also if you have more than one battery I have been told you are supposed to do it for each battery, the only way would be using the SD card direct method, now I personally don't believe it as my batteries always seem to have the correct FW version installed, I'm certain every time you change battery and connect to the drone it checks or updated the FW... otherwise it is super just plain weird... you don't see the message on the controller again saying there is an update, well I never have so once done you basically have done one battery, SD card for the rest.... NO...!!!
Hope that is some help, buy you need to do what you feel comfortable with... Cheers