You can update whenever a newer update is available.
You do need to follow the instructions to a T or you run the risk of major problems that only Humminbird can repair. Instruction are easy to follow.
I haven’t updated mine in years, but nothing is wrong with them that requires an update.
You’ll get mixed reviews with software upgrades as there have been many and for many different reasons.
It would be best to wait a while after the upgrade is released to let others be the Guinee pigs if you in concern of problems.
You can go backward if you choose. Just have to have the older version downloaded to an SD card….
I always retain the previous version(s) on the sd card.
When the system loads it will then ask you if you want to install
the version that is not currently installed.
The wording of the request may be awkwardly stated,
read and answer appropriately.
If you have multiple versions of the install on the card
it will do this every time you boot it.
If the version you want is already loaded, don’t load the undesired version again.