[amw1972]

Connect your phone to your desktop computer...copy ALL files from your 4gb card to a single folder (maybe on your desktop).

then take your phone OFF the computer...replace your 4gb card with your new 8gb card.

reconnect your phone to the computer (wait for the computer to recognize your device)

then take all the contents from that folder that you set up...and just copt them over to the 8gb card. (remember DO NOT just copy that entire folder because your device will not know to "look" in that new folder for your content.)