Tried this it didn't work - but might help somebody else
I purchased a Zumo 550 a little over a year ago and I thought it would have a relative up-to-date set of maps. Since they were getting over a year old I decided to check and found that they were from 2009! This sent me down an upgrade path that ultimately resulted in the purchase of an 8GB SD card since the newer maps won't fit in the memory of the device. None of the posts I found on the upgrade process worked for me, so I created a hybrid that hopefully will help others on the same quest.
Prepare the SD card to spoof your Zumo 550
• Insert the SD in your computer if possible. The process will be much slower if it is inserted into the Zumo 550, but it can be done.
• Use Explorer to create a “\Garmin” subdirectory on the SD card. My SD card was listed as the “E:” drive. It may be different on your computer.
• Connect your Zumo 550 via the USB cable to your computer
• Navigate to the \Garmin directory on the Zumo. Mine was listed as the “F:” drive.
• Copy the “GarminDevice.xml” file from the Zumo 550 to the SD card in the “/Garmin” subdirectory. This allows you to fool the downloader into thinking that the SD drive is your Zumo 550 with lots of available space!
• Eject your Zumo 550 and remove the USB cable.
Download the map update
• Download and start the Garmin Map Updater. The version I used was v3.1.19. It will find your “Zumo 550” (really the SD card). This step is only to give you enough room to download the full update to your computer. DO NOT install the map update to the SD card at this time.
• A few menus in, select “View Options” button.
• Select “Full Coverage of North America” and “Install to Computer Only” and “Leave Installation Files on my computer”
• Start the download process by clicking “OK.” Be patient, this can take anywhere from 30 minutes to several hours.
Prepare the SD card for the map update
• Once the download is complete, delete the GarminDevice.xml file from the SD card and eject the card.
• Eject the SD card from the computer
• Place the card in the Zumo 550 and reconnect the USB cable to the Zumo.
Update the maps on the Zumo 550
• Download and start Garmin MapInstall. It should automatically detect your Zumo
• Select the pull-down menu associated with “device:” and select the “Zumo 550 memory card.” On my unit this was the default.
• Click “Continue”
• Select the regions you want to install. I used the mouse to select all 169 regions which registered as taking 1.8 GB of space on the SD card.
• Click “Continue”
• Click “Install”
• You will now see a message something like, “sending maps to “Memory Card (F:\)” followed by a series of progress messages along with a progress bar.
• Go to bed! The first progress bar indicated that it would only take 8 minutes, but wait, there’s more! The next one said 1 hour 7 minutes remaining.
Final Steps
• The next morning the installer showed “Maps transferred to memory card ….”
• Click “Finish”
• Look on the F: drive under the \Garmin folder. It should show a gmapsupp image file and a GMA file (long numeric name).
• Disconnect the Zumo from the USB. It will restart.
• On the Zumo Look under Tools->Map->Map Info
• You will see both the update (in my case, CN North America NT 2013.30) and the old map (City Navigator North America NT 2009).
• Uncheck the 2009 map
I elected to keep the old map on the device in case something happens to the SD card. That way I at least still have a map on the Zumo.
Hope this helps save some pain and suffering of re(discovering) how to use the SD card on the 550.
