Depending on when you bought your MFD12, you will either have a 40GB or 80GB hard drive. All MFD12s shipped from Furuno warehouses after January 21st of this year contain the 80GB hard drive. Aside from the extra storage space, the only other major difference noticeable to end users was the extra charts (Locked and Unlocked) that were preloaded onto the hard drive. See the list here http://www.furunousa.com/ProductDocuments/NavNet 3D Preloaded Charts (Updated 8-2011).pdf
to review the various chart codes to get an idea of which charts you need, and which ones you don't. It's also a good idea to visit http://www.mapmedia.com/charts-catalog.html
to make sure you download the latest revisions of the Raster/Vector charts and also to download the Satellite PhotoFusion charts for Jersey and the surrounding area. Make sure your system is updated to 2.07, which enables you to use up to a 32GB SDHC card with the MFD series. To check your system software, simply press Menu and scroll down to the My NavNet page, and to the right you will see System Revision: X.XX.
For some live help from the Camas Crew, be sure to visit http://www.navnet.com/tutorials/training_videos/index.html
and there is actually a video dedicated to the instruction of how to manually install/uninstall charts from the system.
If you need further assistance regarding your current software, just drop another reply with what software you have it it isn't current, as that will help us point you in the direction of which updates you need to install and where they can be found.
Good to see someone from the Shore on the forum, I spent many summers down on LBI heading out of Barnegat Inlet. The inlet can get a little ugly during the ebb and flood, but you can't beat the location when it comes time to make a run to the canyons. Feel free to ask any other questions you might have, you've come to the right place.