I can recommend Garmin Homeport, once you get to know your way around it, it is good. But you will need a chart sd card to go with it.
Re updates, do you want to update the chartplotter software or the Blue chart cartography?
a link to the software update page. Download to a PC, unzip the file using the Garmin updater app, copy to an sd card then stick it in your plotter. If you click on the 556 on the linked page you will see the version history, you should make a note of your current software version (tells you on the start up screen) on the plotter and see what new functions etc you gain. Well worth doing.
Re Bluechart updates, I could well be wrong but I think they're only available to the US market. If you want more up to date charts you'll need to buy a G2 vision card, not worth doing IMO