Originally Posted by RVing555
I'll post the results here for anyone else who is interested.
You should have no problem when you simply use a larger (8gb) microSD card. There are a number of posts about this here and a good number of us have already succeeded at doing this. The only "trick" is that you have to copy the "old" backup from the 4gb card onto the new 8gb microSD card before the Navi Toolbox software will recognize the new card and allow it to be updated.
And be prepared for the update to take a while. I did mine overnight and awoke to the completed process.
Also, when I updated mine it contained updates for the whole World of maps and since I don't plan on driving my RV in Europe, Asia or Australia I selected just North America. I don't really plan on driving in Mexico but living in South Texas you never know. Canada is very likely.