Hey Big,
I am not sure a 4GB SD card will do the trick. My original SD card aws 8GB and I bought a comparable SD card of the same capacity.
You need to connect both cards to your computer and copy one folder at a time over to the new blank SD card.
Once complete try your newly created card in your iFly to make sure it works. If everything works as it should you should be able to update either ot both cards using the PC update procedure.
One thing to note is that if you have the streets program it will not work in the copied SD card. The program is tied to the factory SD card and will not operate on another card.
Good Luck