Be safe, transfer your files to your computer, shut the phone down, insert the new sd card, reformat the new card using the built android utility to do so, then move your files from your hardrive to your new sdcard.
This part is tricky...
If you have gigs of music, use "Wifi Pro" to transfer your music, not through the usb cable. Everytime I use an usb cable my mp3s have gotten corrupted...
Should you choose to use wifi pro, only tranfer songs about a 75 (Give or take) to your phone at one time. Transferring music for me is like pulling teeth! (Pulls hair and screams!lol)
P.S. A 64 gig card will work in your phone, should you ever buy one. You would have to follow the procedure I outlined above. I always format a new card with the phone, not a computer.