It is always a good idea to have your present version of software on a separate formatted SD card so that if something goes awry in the update process...the unit can be reverted back to a "working" software version...

So in the case of 2 different units..
1 SD card with present version of software for the 597...
1 SD card with new version of software for the 597....

Then format the cards and do the same for the 798..

Or have 2 extra SD cards (total of 4)...
1 with present version of software for the 798..
1 with new version of software for the 798...

SD cards are cheap... A few extra $$ in SD cards can save a lot of aggrivation when having problems with software updates..(especially on the water)...

Rickie