DaveW
As Wayne P stated Humminbird will not update the map programs on their units.
The best way to go is to purchase a Navionics HotMaps chip for your unit and fishing area. They are expensive starting out at $100, but they are worth the purchase.
I would check the lakes that you fish on your unit and then go to Bass Pro Shops or a boat show and get some help from Navionics to see if the maps are much better then what is on your unit.
If you purchase a chip most likely it will be a long while before you have to update it unless you are on a very popular lake that they make frequent updates too.
Navionics does not publish their updates so that we can make a knowledgeable decision on whether or not it is time to purchase a new chip.
George