the only things stored on the SD card is cache data from apps and any pictures and music you load on their yourself.
if you have any apps installed to the SD card, move them to internal storage.
after doing that, connect it to your PC, transfer all the folders into the new card (after you format the new card) and pop the new card in your phone and your done!!!
text messages and anything else u do stay on the phone, except if your changing roms, then youll need to back them up with Go SMS