The chart data is contained in a file named gmapsupp.img in the "Garmin" or "Map" folder of the SD card. This file needs to be replaced with the latest version, follow the below procedure to safely replace the file with the new version. You must have an SD card reader attached to your computer, or built in (a lot of notebooks have these as standard). On the Nuvi you can alternatively copy the file directly from the Nuvi folder in the Corrib Chart installation folder to the "Map" folder on the Nuvi itself.
To update your SD card simply copy the new gmapsupp.img file into the "Garmin" or "Map" folder on your SD card.
NOTE. The newer versions of the chart have contouring at 10ft intervals. If the chart seems a little "busy" please reduce the detail level. The detail will still be there at higher zoom levels, but will not be so cluttered at low zoom levels. This needs to be experimented with as it is a matter of personal preference.