I wondered about this but you need the files appropriate to your Zumo, and the download site mentioned on that link has long since disappeared.
There is a site called Wayback MAchine that systematically takes copies of other websites at intervals, and there are copies on that. I also prepared some detailed notes on how to use it. I'll go hunting, but probably not today.
You need 3 files - 2 programs and a data file.
The programs are available from
www.javawa.nl/ge-upgrade590to595.html
Click the link for SoftwareMissing (for Updater) and the link for RGNTool
Yes - I know the link is for the upgrade from a 590 to a 595 - but the process is identical for your machine - except the name of the gcd file.
You also need the GCD file for your machine. You used to be able to get them from gawisp.com/perry - but that site has gone.
Wayback machine (google it) has archive versions, and I checked it out this morning and managed to download a file. Now it says that it cannot find any ! It shows the links to the files but they no longer work for me.
I can't believe that they have just disappeared. It is possible that they have deleted them from the server, and I managed to get hold of a cached version
Basically you need the rgntool to convert the gcd file to an rgn file.
You need the updater to install the rgn file onto your Zumo.
Ive got notes that use the instructions that are now on the javawa site (above), which I have worked through and illustrated and added more useful detail.
But first you have to get hold of the gcd file from somewhere. edit: I managed to find a few links that worked on a recent backup - but the 396 was not listed.
Make another phone call to tech support. ask questions like if you get someone elses copy of GUPDATE.gcd - will that work ? (Someone on here suggested that it worked for them - they sent him a copy.
Have owned Zumo 550, 660 == Now have Zumo XT2, XT, 595, 590, Headache
Use Basecamp (mainly), MyRouteApp (sometimes), Competent with Tread for XT2, Can use Explore for XT - but it offers nothing that I want !
Links:
Zumo 590/5 & BC . . .
Zumo XT & BC